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Opportunities for fully funded PhD or EngDoc research projects are available in all fields of research within the School. You may search for current projects on this page. APPLY HERE for a PhD Place.
PhD in Photonics
PhD in Condensed Matter
PhD in Astrophysics
Search current PhD opportunities in the School of Physics & Astronomy:-
All ---- Bonnell, Prof Ian [2] Braunecker, Dr Bernd [4] Brown, Prof Tom [3] Cassettari, Dr Donatella [2] Cizmar, Dr Tomas [1] Cyganowski, Dr Claudia [2] Dholakia, Prof Kishan [3] Di Falco, Prof Andrea [3] Gather, Prof Malte [4] Helling, Dr Christiane [1] Hicks , Dr Clifford [1] Hooley, Dr Chris [4] Horne, Prof Keith [1] Huxley, Prof Andrew [1] Jardine, Prof Moira [3] Keeling, Dr Jonathan [2] King, Prof Phil [5] Koenig, Dr Frieder [2] Lee, Prof Steve [1] Lovett, Dr Brendon [2] Mackenzie, Prof Andy [4] Mazilu, Dr Michael [1] Ohadi, Dr Hamid [2] Penedo-Esteiro, Dr Carlos [1] Robertson, Dr Duncan [2] Rost, Dr Andreas [1] Samuel, Prof Ifor [9] Schubert, Dr Marcel [1] Schulz, Dr Sebastian [2] Scott, Prof Jim [2] Smith, Prof Graham [1] Tojeiro, Dr Rita [2] Turnbull, Prof Graham [7] Wahl, Prof Peter [5] Wild, Dr Vivienne [4] Woitke, Dr Peter [3] Wood, Dr Kenny [4] Zhao, Dr Hongsheng [3]
All ---- Active Galactic Nuclei [1] ARPES on correlated materials [4] Atmospheres of Very Low Mass Objects [1] Biophotonics Collaboration [3] Correlated Electron Systems [3] Dark Matter in Galaxies [3] Dynamics of Star Formation [5] Experimental quantum optics [2] Extra-Solar Planets [1] Galaxy Populations and their Evolution [4] Millimetre-wave physics and THz technology [3] Nonlinear Optics Group [1] Optical Manipulation Group [2] Organic Photonics [4] Organic semiconductor centre [6] Polymer optoelectronics [6] Protoplanetary Discs [3] Quantum optics and information [3] Quantum order at extreme conditions [1] Semiconductor physics [2] Soft matter photonics [4] Stellar Magnetic Fields [3] Superconductivity and Magnetism [2] Synthetic Optics [4] Theory of Condensed Matter - BHB [4] Theory of Condensed Matter - CAH [4] Theory of Condensed Matter - JMJK [2] Theory of Quantum Nanomaterials [2] Tunneling Spectroscopy of Strongly Correlated Electron Materials [5] Ultrashort pulse lasers [2]
All ---- Photonics Astrophysics Condensed Matter
Galactic Dark Matter Effects from New Physics of Modified Gravity or Dark Energy
Zhao, Dr Hongsheng - hz4@st-andrews.ac.uk
We explore alternatives to the Cold Dark Matter framework by adding new physics in Dark Matter.
The new physics could include Modified Gravity or matter with fifth force interactions.
Several rare coincidences of scales in standard particle physics
are needed to explain why the negative pressure of the cosmological dark energy (DE)
(i) coincides with the positive pressure of random motion of dark matter (DM) in bright galaxies,
(ii) is within order of magnitude of the energy density of neutrinos, if it is allowed to have a mass of eV.
(iii) why Dark Matter in galaxies seems to follow the Tully-Fisher-Milgrom (MOND) relation of galaxy rotation curves, rather than the CDM predicted profile.
The aim is to link empirical dark matter constraints in galaxies with the cosmology.
The work can be purely theoretical using the Euler-Lagrangian approach. Or empirical by fitting galaxy velocity distributions and Gravitational Lensing data.
Dark Matter in Galaxies
A bad case of split personality
Jardine, Prof Moira - mmj@st-andrews.ac.uk
Recent studies of the magnetic fields of very low mass stars shows a strange and so far unexplained behaviour. Some have strong, simple magnetic fields, and some have much weaker, complex, solar-like field magnetic fields. We do not fully understand why this difference occurs, but this project involves using the maps of the magnetic fields of these star to explore the physics of their coronae and winds and to examine the impact on any orbiting planets.
Stellar Magnetic Fields
A complete census of rapidly quenching galaxies over cosmic time
Wild, Dr Vivienne - vw8@st-andrews.ac.uk
It has been known since the 1920's that most local galaxies can be morphologically classified as spirals or ellipticals. In the last century advancing galaxy surveys have demonstrated that morphology strongly correlates with many other galaxy physical properties: spiral galaxies are typically forming stars, contain cold gas and dust, live in less dense environments, and have modest-sized central black holes, whereas elliptical galaxies are "quenched" (not forming stars), surrounded by hot gas, live in denser environments, and have larger black holes. Despite precise statistical characterisation of these properties throughout much of cosmic history, the underlying physics that separates galaxies into star forming vs. quenched, with all attendant correlations, remains unclear. Understanding the *pathways* by which galaxies quench is a crucial outstanding question at the heart of modern galaxy formation and evolution, impacting a range of astrophysical studies from star formation and interstellar medium to dark matter and dark energy.
In this project we will combine the analysis of optical/NIR photometry and upcoming spectroscopy from the new MOONS NIR spectrograph on the VLT to identify and characterise the properties of rapidly quenched galaxies from redshifts of 0 to 2 in the real and simulated Universes. We will study their environment and gas properties to identify trends that should be reproducible in advanced cosmological hydrodynamic simulations. Comparison of data and simulations will elucidate the role of rapid quenching in the build up of the red sequence.
This project will work closely with Romeel Dave in Edinburgh (rad@roe.ac.uk), who runs the SIMBA and MUFASA galaxy evolution simulations. Real and mock data is in hand to commence the project. During the lifetime of the project new data will become available from the MIGHTEE survey (HI and radio SFRs) and VLT/MOONS (rest-frame optical spectroscopy of redshift 1-2 galaxies).
This is an exciting time to embark on such a project, with upcoming MOONS data set to revolutionise our understanding of quenching galaxy properties, and simulations such as Simba finally producing galaxies with similar colours to observed rapidly quenched galaxies.
MOONS: https://www.eso.org/sci/facilities/develop/instruments/MOONS.html
MIGHTEE: https://arxiv.org/abs/1709.01901
http://adsabs.harvard.edu/abs/2018MNRAS.473.1168R
http://adsabs.harvard.edu/abs/2016MNRAS.463..832W
http://adsabs.harvard.edu/abs/2017MNRAS.471.1671D
Galaxy Populations and their Evolution
Angular momentum loss and mass loading of stellar winds - slingshot prominences in action
Many solar-like stars show cool, dense clouds of gas trapped within the million-degree plasma of their outer atmospheres (or coronae). These so-called ``slingshot prominences'' carry away angular momentum when they are ejected and also are also responsible for mass-loading of the stellar wind. As a result, they may form an important part of the spin-down of young stars, and their impact on orbiting planets may lead to enhanced stripping of the planetary atmosphere.
Annihilation of Dark Matter
A main diagnostic of the particle dark matter is its annihilation rate, which depends sensitively on the dark matter density profile. The student will explore various density models of the dark matter, taking into account the effects of black holes and baryonic dynamics.
CHAMELEON -- Virtual laboratories for exoplanets and plane-forming disks
Helling, Dr Christiane - ch80@st-andrews.ac.uk
Woitke, Dr Peter - pw31@st-andrews.ac.uk
Retrieving (from data), predicting (from detailed models) and thereby understanding the link between the chemical composition of planet-forming disks and exoplanet atmospheres is a challenging task. In this Marie-Curie Innovative Training Network (MC-ITN), we focus on the development of Virtual Laboratories which will be the crucial tool to analyse in detail current and future disk and exoplanet observations. Virtual laboratories play a key role in simulating yet unexplored physico-chemical environments. In addition, while observational data are often hampered by incompleteness in terms of frequency coverage, time coverage, different instrument systematics when combining data etc., Virtual Laboratories can overcome these shortcomings and are a key pre-requisite to answer the questions whether our Solar System is unique and how life emerged.
The CHAMELEON consortium advertices 15 PhD places throughout Europe:
https://chameleon.wp.st-andrews.ac.uk/recruitment/
ESR 5, 6, 7 and 9 will be in St Andrews.
The CHAMELEON students will be part of the St Andrews Centre for
Exoplanet Science: https://www.st-andrews.ac.uk/exoplanets
Atmospheres of Very Low Mass Objects
Extra-Solar Planets
Protoplanetary Discs
Charge conservation and cloud formation in planet atmospheres
As result of formation and evolution processes, exoplanets can have hugely different properties, e.g. giant gas planets, rocky planets, mini-neptunes. Today's best constrained exoplanets are short period, hot Jupiters which show `muted' molecular features, enhanced
Rayleigh scattering slopes in the optical, and dynamic features like onsets in the brightest optical emission of the planet. These features arise from a globally circulating and cloud forming atmosphere (Lee et al. 2016 MNRAS 640) which is driven by an intense irradiation field from the host star. Both, dynamics and radiation ionise cloud particles (Helling et al. 2011, ApJ 737; Rodíguez-Barrera et al. 2018, A&A 618).
In order to understand the myriad of observational data from present (HST, Spitzer) and future space missions (CHEOPS, JWST, Ariel, PLATO), a thorough understanding of the cloud formation processes is required. The key processes to cloud formation, nucleation and surface growth, will be studied under the effect of ionisation. The effect of ionised particles is essential for cloud formation on Earth but little is known for exoplanets.
This project is part of the Marie Sklodowska-Curie Innovative Training Network (ITN) CHAMELEON "Virtual Laboratories for Exoplanets and Planet Forming Disks" (chameleon.wp.st-andrews.ac.uk). The ITN combines the expertise of eight European research institutes (Universities of St Andrews, Groningen, Copenhagen, Edinburgh, Leuven and Antwerp, the Max-Planck Institute in Heidelberg and the Netherlands Institute for Space
Research) to cover all relevant aspects for this complex modelling task, joining the expertise in planetary atmospheres and protoplanetary disks, including observation and interpretation. The network will consist of 15 Early Stage Researchers (PhD students) and the respective supervisors/local research groups. For a complete list of all open PhD positions within this training network please visit http://chameleon.wp.st-andrews.ac.uk/recruitment/.
Determining the origins of galaxy bimodality using hierarchical Bayes methods
How galaxies form and evolve is one of the outstanding questions of modern astrophysics. We have known for many decades that massive galaxies come in two main types - elliptical/quiescent and spiral/star-forming. However, it remains largely unknown why some galaxies are still forming stars while others are "red and dead". Extremely large galaxy surveys are providing an increasingly detailed census of both local and distant galaxies. Considerable progress is being made on quantifying the changing demographics of the galaxy population over the majority of the age of the Universe, but significant improvements in methods are required to dramatically improve our understanding of the physics behind the observable properties of galaxies.
In the last decade a Bayesian approach to the fitting of sophisticated models to high quality spectra and/or multiwavelength photometry has become common place in the analysis of galaxy spectral energy distributions (SEDs) at all redshifts (Walcher et al. 2011). The result is robust physical properties, such as galaxy stellar mass, dust content and star formation history, together with well quantified degeneracies between these parameters. However, by treating galaxies as independent entities to determine their physical properties, we are missing vital population information. A better approach would be to treat galaxies as a population of objects with a common origin and common underlying variables. This could tighten constraints on the physical properties of individual galaxies as well as the underlying relationships that impact the life of galaxies. It could also allow us to extract information from larger surveys with lower quality observations.
Hierarchical Bayes techniques have been used in the astronomical literature to solve problems as diverse as quasar redshift estimation (Bovy et al. 2011), exo-planet orbit analysis (Hogg et al. 2011), properties of supernovae light curves (Mandel et al. 2009), and photometric redshifts (Leistedt et al. 2016). They differ from standard Bayesian methods by fitting the entire dataset in a coherent manner, instead of single objects as entirely independent entities. By applying these methods to galaxy evolution studies, we will improve our ability to break degeneracies between physical parameters and understand the underlying processes governing galaxy evolution. These methods could be applied to e.g. complete populations of galaxies in spectroscopic or photometric surveys, or entire integral field datacubes of single galaxies.
This interdisciplanary project will be jointly supervised by Drs Vivienne Wild and Michail Papathomas in the Schools of Physics and Astronomy and Mathematics and Statistics respectively. Dr Wild has built her career around developing and applying novel statistical techniques to explore datasets on galaxy evolution, focussing most recently on understanding the nature of post-starburst galaxies. Dr Papathomas is an expert in Bayesian modelling, both in the development of new methods and their application to a wide variety of datasets.
Large extragalactic datasets are already available for analysis, both at low and high redshift. The School of Physics and Astronomy is a member of the UK participation group in SDSS-IV, the fourth generation of Sloan Digital Sky Surveys, a large international collaboration encompassing several astronomical surveys. The methods developed during the project could also be applied to upcoming datasets to which the group has proprietary access such as DESI bright galaxy survey, LSST science verification data and VLT/MOONS near-infrared spectroscopic survey.
The project involves the development of statistical techniques to make them applicable to astronomical datasets. This project would suit students with a background in (astro)physics but strong aptitude for maths and statistics, and students with a background in maths or statistics and interest in astrophysics.
For more information please contact Dr Vivienne Wild and Dr Michail Papathomas (vw8@st-andrews.ac.uk, M.Papathomas@st-andrews.ac.uk).
Bovy J., Myers A. D., Hennawi J. F. et al. arXiv:1105.3975
Hogg D. W., Myers A. D., Bovy J., 2010, ApJ, 725, 2166
Leistedt B., Mortlock D., Peiris H., 2016, MNRAS, 460, 4258
Mandel K. S.; Wood-Vasey W. M., Friedman A. S., Kirshner R. P., 2009, ApJ, 704, 629
Walcher C. J., Groves B., Budavri T., Dale D., Ap&SS, 2011, 331, 1
SDSS-IV www.sdss.org
LSST www.lsst.org
DESI www.desi.lbl.gov
MOONS https://vltmoons.org/science-2/
Diffuse ionized gas in galaxies
Wood, Dr Kenny - kw25@st-andrews.ac.uk
Extensive layers of diffuse ionized gas are observed in the Milky Way and other galaxies. This project will study the structure, ionization, heating, and dynamics of diffuse ionized gas using our newly developed radiation hydrodynamics codes that incorporate feedback processes including photoionisation, stellar outflows, and supernovae. Output from our 3D rad-hydro simulations will be compared with emission line observations of the diffuse ionised gas.
Dynamics of Star Formation
Dissecting galaxies in transition
The number density of `red and dead' elliptical galaxies increases with cosmic time, meaning galaxies must be transitioning from star-forming disks. In this project we will use the SDSS-IV MaNGA integral field survey alongside mock observations of hydrodynamic simulations to move beyond demographics and pin down which physical processes are responsible for this transition, as a function of stellar mass and environment.
Massive galaxies in the nearby Universe typically fall into two distinct populations (e.g. Strateva et al. 2001; Baldry et al. 2004): actively star-forming disk galaxies, and `red and dead' elliptical galaxies with little or no signs of ongoing star formation. The bimodality in the star-forming properties of massive galaxies has existed since at least z~2 (Tomczak et al. 2014), and the strong correlation between star-forming properties and morphology holds to a similar epoch.
The increasing number density of red-sequence galaxies with cosmic time at fixed stellar mass (e.g. Moutard et al. 2016) tells us that galaxies move from the blue-cloud to the red-sequence by having their star formation halted (`quenched'). Coincidentally, the typical star formation rate of galaxies decreases as they exhaust their gas supplies, but this process is unable to account for the alteration in the galaxies' morphologies. Many different mechanisms have been proposed to partly or wholly explain the build-up of the quenched elliptical population with time, such as gas stripping, merger induced starbursts, AGN feedback and morphological quenching.
Catching galaxies that are in the act of transition, and studying both their evolving demographics and their properties in detail, alongside mock observations from state-of-the-art simulations, are the ways to make further progress (Wild et al. 2009). These objects are rare, and only recently have surveys been large enough for us to be able to constrain the number density evolution of green-valley and post-starburst galaxies, alongside the quiescent galaxies we expect them to evolve into.
The advent of highly multiplexed integral field surveys, alongside well developed hydrodynamic galaxy simulations, means the time is perfect for a fully encompassing study of all types of candidate-transition galaxies. The fossil record of a galaxy's formation history is encoded in its morphology, stellar kinematics, stellar populations and dust, ionised gas content and kinematics. The MaNGA survey provides access to all of these, alongside robust control samples, volume correctable number densities, a wide range of environments and stellar masses. Importantly, comparison to both idealised and cosmological hydrodynamic simulations is now possible, converted into mock data cubes to be analysed in exactly the same way as the data.
In this project we will perform an integrated analysis of the morphologies, shapes, spatially resolved kinematics and stellar populations of the largest ever sample of local post-starburst, blue-ellipticals, red-spirals and green-valley galaxies observed with an integral field unit, alongside large sets of control samples and hydrodynamic simulations. We will aim to understand what are their ancestors and descendants and thereby understand whether they are truly transitioning populations, and on what timescales. We will use these results to interpret data from high-redshift surveys, where post-starburst galaxies are far more common and potentially important for building the present-day galaxy bimodality (Wild et al. 2016).
Strateva et al. 2001, AJ 122, 1861
Baldry et al. 2004, ApJ 600, 681
Tomczak et al. 2014, ApJ, 783, 85
Moutard et al. 2016, A&A, 590, 103
Wild et al. 2009, MNRAS, 395, 144
MaNGA survey : http://www.sdss.org/surveys/manga/
Echo Mapping of Black Hole Accretion Flows in Active Galactic Nuclei
Horne, Prof Keith - kdh1@st-andrews.ac.uk
This project qualifies as an�STFC studentship in Data-Intensive Science.
Light travel time delays enable micro-arcsecond mapping of accretion discs and broad emission-line regions around the super-massive black holes in the nuclei of active galaxies. Using our share of time on the LCOGT robotic telescope network, along with data from HST, Swift and Kepler satellites, we are monitoring spectral variations of Active Galactic Nuclei to measure black hole masses, accretion rates, and luminosity distances. By decoding information in the reverberating emission-line profiles, we make 2-dimensional velocity-delay maps of broad emission-line regions, mapping the velocity field and ionisation structure of the accretion flows. The student will acquire and analyse such datasets, fitting parameterised models using MCMC methods, image reconstruction using Horne maximum entropy fitting code MEMEcho, and photo-ionisation codes such as Ferland's Cloudy.
Active Galactic Nuclei
Exoplanet atmospheres: Microphysics of cloud formation
As result of formation and evolution processes, exoplanets can have hugely different properties, e.g. giant gas planets, rocky planets, mini-neptunes and possibly carbon-rich planets. The understanding of these objects is, to a large extent, hampered by clouds obscuring their atmospheres. Clouds play a key role for the atmospheric dynamics and
chemistry, as they are important opacity sources and deplete the local gas phase (Helling 2019, Exoplanet Clouds, Annual Review of Earth and Planetary Sciences 47). In order to understand the myriad of observational data from present (HST, Spitzer) and future space
missions (CHEOPS, JWST, Ariel, PLATO), a thorough understanding of the cloud formation processes is required. The process that kicks off the cloud (or dust particle) formation is the nucleation process by which gas-phase species grow to larger clusters which then grow into condensation seeds. This project aims to conduct theoretical work on the nucleation process that is equally applicable to modelling cloud formation in exoplanets and brown dwarfs, and to dust formation in AGB stars (Decin et al. 2017, A&A 608). We will combine computational
chemistry calculation with physical cloud formation modelling (Helling & Fomins 2017, PhiTransA 371).
The selected PhD students will be offered a fully funded PhD place with a required training secondment for this position foreseen at the University of Leuven, with an additional short training at the University of Copenhagen. The funding will be commensurate to the standard scale for PhD students in according to the Marie-Curie funding rules. The successful PhD applicants will have to register at, and comply with, the regulations of the St Leonard's Postgraduate College at the University of St Andrews and the Arenberg Doctoral School of
the KU Leuven. The successful PhD applicants will follow a doctoral programme including personal training in management, science communication, and teaching.
Feedback in young stellar clusters
Cyganowski, Dr Claudia - cc243@st-andrews.ac.uk
Most stars form in clusters, where energetic feedback from massive
(proto)stars--including outflows, ionization, heating, and
winds--shapes the environment and impacts accretion. The relative
importance of different feedback processes is a key outstanding
issue in our understanding of massive star formation.
The aim of this project is to conduct the first large-scale
observational study of the role and physics of feedback in massive
(proto)clusters. This will involve analyzing high-resolution data
from recently-upgraded (sub)mm and cm-wavelength interferometers, in
particular the Submillimeter Array (SMA), the Jansky Very Large Array
(VLA), and, potentially, the Atacama Large Millimeter/sub-millimeter
Array (ALMA). The observational results will be compared with
simulated observations of numerical models of massive star and
cluster formation.
Feedback processes in star forming regions and the interstellar medium
This project will use (and futher develop) our new radiation hydrodynamics codes to syudy the effects of stellar feedback on the structure, dynamics, and star formation rates in star forming regions (parsec sizescales) and the interstellar medium (kiloparsec sizescales). Feedback processes that are readily incorporated into our codes include photoionisation, radiation pressure, dust heating, stellar outflows, and supernovae. In addition to studying these processes in star forming regions, the new numerical codes are also applicble to numerical studies of galactic outflows and the impact of feedback processes and leakage of ionising radiation into the intergalactic medium.
Informal enquiries to Kenny Wood: kw25@st-andrews.ac.uk
Grain Charges and Lightning in Protoplanetary Disks
The thermo-chemical state of circumstellar disks determines the composition of planets that form in them, and is hence the key to understand exoplanet diversity. Yet, the temperature and chemical composition of the gas in these disks is not known, in particular the properties of the gas in the midplane inside of ∼10 au (Woitke et al. 2018, A&A 618, 57), where most of the planets form. In this project, we want to study grain charging processes in protoplanetary disks and their feedback on gas ionisation and observation of line emission by molecular ions. Based on a moment method developed in Thi et al. (2018, arXiv 1811.08663), we want to compute the size-dependent charge distribution function of grains f(a,Z) in the disk, where a is the grain radius and Z its charge, based on our state-of-the-art disk modelling software ProDiMo (Woitke et al. 2016, A&A 586, 103). In particular, we want to include the so-called tribo-electric effect, where grains undergo frictional charging when they collide with each other in a turbulent environment. In combination with dust settling, this effect is known to cause electrification of volcano plumes and, more general, lightning in the Earth atmosphere (Helling et al. 2016, Survey in Geophysics 37, 705). It is hence the aim of this project to find out in how far this mechanism also applies to protoplanetary disks, and could change the chemical composition and ionisation in disks.
Innovative Training Network (ITN):
This project is part of the Marie Sklodowska-Curie Innovative Training Network (ITN) CHAMELEON "Virtual Laboratories for Exoplanets and Planet Forming Disks" (http://chameleon.wp.st-andrews.ac.uk/). The ITN combines the expertise of eight European research institutes (Universities of St Andrews, Groningen, Copenhagen, Edinburgh, Leuven and Antwerp, the Max-Planck Institute in Heidelberg and the Netherlands Institute for Space Research) to cover all relevant aspects for this complex modelling task, joining the expertise in planetary atmospheres and protoplanetary disks, including observation and interpretation. The PhD position is fully funded for a period of 3.5 years. All students will obtain double degrees. Training secondment for this position is foreseen for six months at the Niels-Bohr Institute in Copenhagen, under the supervision of Prof. Uffe G. Jørgensen, see www.astro.ku.dk/~uffegj. As Marie Sklodowska-Curie fellows, you will receive generous benefits, including a fixed salary with additional mobility and family allowances. The network will consist of 15 Early Stage Researchers (PhD students) and the respective supervisors/local research groups. For a complete list of all open PhD positions within this training network, including those of our European partners, please see http://chameleon.wp.st-andrews.ac.uk/recruitment/.
We seek an excellent student with a strong background in physics or astrophysics. Successful candidates must hold a Masters degree or equivalent by the starting date of the position. Previous research experience on planet forming disks and/or astrochemistry, and a track record of team work/mobility will be important criteria for the selection. This is a computational project: some prior knowledge of coding would be useful (e.g., Python and Fortran). Note that the general eligibility and mobility rules of Marie Sklodowka-Curie Actions apply, i.e. applicants must not have resided or carried out their main activity (work, studies, etc.) in the country of the main host institution (in this case the UK) for more than 12 months in the 3 years immediately before the recruitment date. If you have been residing in the UK, please consider to apply to the open positions of our European partners (http://chameleon.wp.st-andrews.ac.uk/recruitment/).
Your application package should contain (i) a CV including publication list if applicable, (ii) a statement of interest (max. one page, including a brief description of research interests and relevant experience), (iii) copies of university grades, certificates and/or diplomas, (iv) two letters of reference to be sent by the application deadline, (v) a statement that confirms that you undestood the requirements of the joint degree and the Marie Sklodowska-Curie mobility criteria as outlined at https://chameleon.wp.st-andrews.ac.uk/recruitment/. Use the portal of the School of Physics & Astronomy in St Andrews University https://www.st-andrews.ac.uk/physics/prosp_pg/phd/index.php to upload your application documents. The application deadline is 06/01/2020, however, applications that arrive after this date may also be considered until all ITN positions are filled. The foreseen start date is September 2020.
Machine Learning from Complex Disk Models
Molecular emission features observed in the near and mid infrared, for example with the VLT and JWST, will allow us to determine the chemical composition of the gas in protoplanetary disks in the planet-forming regions within 10 au around new-borne stars. This project will combine our previous expertise in modelling the line radiative transfer, chemistry and heating/cooling balance in disks, see Woitke et al. (2016, A&A 586, 103) with new machine learning techniques developed in the exoplanet community, e.g. Zingales & Waldmann (2018, AJ 156, 268). Neutral networks (NNs) will be trained on the predictions by tens of thousands of complex thermo-chemical 2D disk models, where we will apply the radiative transfer code FLiTs (Woitke et al. 2018, A&A 618, 57) to post-process the ProDiMo results to identify the spectral signatures. Using an algorithm developed for the ARCiS code (artful modelling of cloudy exoplanet atmospheres, author M. Min), these NNs will enable us to retrieve the chemical composition and the physical disk parameters, including their errorbars, from the observations. We can then use these new machine learning algorithms to quickly predict the emergent near-mid infrared line emission spectra from disks as function of physical parameters like UV irradiation, dust/gas ratio and element abundances, capable to thoroughly fit and analyze JWST data to determine the physical disk parameters and their observational uncertainties, taking into account all degeneracies.
This project is part of the Marie Sklodowska-Curie Innovative Training Network (ITN) CHAMELEON "Virtual Laboratories for Exoplanets and Planet Forming Disks" (http://chameleon.wp.st-andrews.ac.uk/). The ITN combines the expertise of eight European research institutes (Universities of St Andrews, Groningen, Copenhagen, Edinburgh, Leuven and Antwerp, the Max-Planck Institute in Heidelberg and the Netherlands Institute for Space Research) to cover all relevant aspects for this complex modelling task, joining the expertise in planetary atmospheres and protoplanetary disks, including observation and interpretation. The PhD position is fully funded for a period of 3.5 years. All students will obtain double degrees. Training secondment for this position is foreseen for 12 months at SRON in Utrecht, The Netherlands, working with Dr. Michiel Min. In addition, regular research visits of the research group of Prof. Inga Kamp are planned at the Kapteyn Institute in Groningen, The Netherlands. As Marie Sklodowska-Curie fellows, you will receive generous benefits, including a fixed salary with additional mobility and family allowances. The network will consist of 15 Early Stage Researchers (PhD students) and the respective supervisors/local research groups. For a complete list of all open PhD positions within this training network, including those of our European partners, please see http://chameleon.wp.st-andrews.ac.uk/recruitment/.
We seek an excellent student with a strong background in physics or astrophysics. Successful candidates must hold a Masters degree or equivalent by the starting date of the position. Previous research experience on machine learning, astrochemistry and/or radiative transfer, and a track record of team work/mobility will be important criteria for the selection. This is a computational project: some prior knowledge of coding would be useful (e.g. Python and Fortran). Note that the general eligibility and mobility rules of Marie Sklodowka-Curie Actions apply, i.e. applicants must not have resided or carried out their main activity (work, studies, etc.) in the country of the main host institution (in this case the UK) for more than 12 months in the 3 years immediately before the recruitment date. If you have been residing in the UK, please consider to apply to the open positions of our European partners (http://chameleon.wp.st-andrews.ac.uk/recruitment/).
Application documents:
Mass Distribution of the Galaxy
The mass distribution of the Galaxy is being / will be mapped out in great detail in the next decade with the numerous surveys of the Galaxy, including Segue, RAVE, GAIA, and completed ones like 2MASS, DENIS. A model for the potential and phase space of the galaxy is essential to bring various pieces of information together. The student will develop such models building on experience from existing models.
New physics for Dark Matter via Modified Gravity/Dark Energy
New Physics for Galactic Dark Matter via Modified Gravity/Dark Energy
Observations and simulations of massive star formation
While the details of the formation mechanism of massive stars remains uncertain, many of the proposed scenarios ultimately rely on accretion via a rotationally supported circumstellar disk or torus. The circumstellar environment of a massive star is subject to feedback processes including photoionisation, radiation pressure on dust, jets and outflows. These feedback effects leave their imprint on the observed images, spectra, and velocity distributions of the circumstellar environment, thus providing further clues to the formation mechanisms in different environments for stars of different masses. This project will combine new high spatial and spectral resolution observations of massive star forming regions together with radiation transfer and radiation hydrodynamics simulations to model the data in order to build up a detailed picture of the environment and conditions leading to massive star formation.
Star formation in dwarf galaxies
Bonnell, Prof Ian - iab1@st-andrews.ac.uk
This project is to develop the first models of resolved star formation on galactic scales. This will involve modelling a full galactic potential and how it drives the formation of molecular clouds and the onset of gravitational collapse and star formation. feedback from ionisation and supernova will be included to assess molecular cloud lifetimes and star formation efficiencies.
Star-Planet Interaction
Tau Boo is the only star for which we have been able to track the full cyclic reversal of the stellar magnetic field. This system is also well-known, however, because it hosts a Hot Jupiter that is so close to the star that it may lie within the stellar corona. What is the nature of the interaction between the star and planet in this case and is it related to the puzzling nature of the very short magnetic cycle? This project will investigate tau Boo and other similar star-planet systems.
The gas content of the cosmic web
Tojeiro, Dr Rita - rmftr@st-andrews.ac.uk
Galaxies have a complex relationship with surrounding gas. Cosmic-web filaments take on especially important roles for halo and galaxy growth: simulations indicate that around 40 percent of the Dark Matter in the Universe is found within filaments, and they act as conduits that feed Dark Matter and neutral, cold gas into halos and galaxies. The neutral cold gas, once accreted onto a galaxy, will almost always form stars, at which point it becomes easily detectable via starlight. However, although a key player in the formation and growth of galaxies, we know astoundingly little about the gas component of the cosmic web, before it reaches the vicinity of a galaxy.
In this project, you will cross-correlate excess absorption in the spectra of distant quasars with filaments detected via the positions of galaxies, to understand the gas content of the cosmic web, far from the influence of dark matter halos. You will work with eBOSS and DESI data, which together provide the densest sample of lines of sight that pierce the low-redshift cosmic web. Your observational work will be complemented by work in cosmological hydrodynamical simulations
The host galaxies of luminous AGN
Understanding the link between active galactic nuclei and their host galaxies has become one of the most pressing problems in extragalactic astronomy. What is the impact of the energy released by the AGN on the host galaxy? There is lots of circumstantial evidence that the impact should be substantial, but direct observational evidence is scarce.
One of the key problems is that luminous AGN easily outshine their host galaxies, making it difficult to ascertain what the galaxy properties are. Much work has been done on trying to reveal their morphology (for example, are they merger remnants?), but there have been limited attempts to understand their stellar populations. Stellar populations are key to uncovering their recent history to reveal whether they have recently suffered a sharp decrease in star formation, which would indicate a significant AGN feedback effect.
In collaboration with Prof. Paul Hewett (IoA Cambridge) and Dr Carolin Villforth (Bath) we have recently developed a novel method to decompose AGN spectra into their broad line AGN and host galaxy components. This PhD project will exploit those methods to reveal the stellar populations of QSO hosts as a function of luminosity, eddington ratio and presence/absence of QSO outflow signatures, comparing to control samples to understand the impact of the QSO on the host galaxy.
Triggering of star formation
There are several outstanding issues in current models of star formation. One of these is the role of feedback from young stars in producing subsequent generations of young stars. Triggering of star formation through supernova events is likely to be the dominant mechanism. Numerical simulations of SNII impacting on molecular clouds and the triggering of star formation will be used to develop physical models, and ultimately observational predictions and tests of the process.
Unveiling the role of environment on the growth of galaxies and dark-matter halos
One of the challenges in galaxy evolution is to understand the evolutionary paths of different types of galaxies. Although stellar mass (observationally) and halo mass (in simulations) display a dominant role in the formation and evolution of galaxies, the role of environment is less well-understood. This is largely due to the difficulty in defining "environment", and in estimating it from observations.
This project will combine data from three datasets to investigate the role of environment in the local Universe with unprecedented clarity. Local environment will be estimated with the forthcoming DESI survey (currently commissioning - Nov 2019). DESI will observe a high-density, high-completeness sample of galaxies out to z=0.4 over 14,000 sq degrees, starting in 2020. By combining this exquisite dataset with integral field spectroscopy from the MaNGA survey, and deep imaging for the Legacy imaging surveys, you will investigate the role of environment for a variety of physical estimators (such as overdensity over a variety of scales, satellite/central classification, cosmic web estimators and projected correlation function) on integrated and resolved properties of galaxies. Supplementing your observational work with cosmological hydrodynamical simulations, you will understand the implications of your results for the evolution of halos, galaxies and the galaxy-halo connection.
Coexistence or Competition: Resolving the phase diagram of unconventional superconductors through atomic scale imaging of emergent phases
Wahl, Prof Peter - gpw2@st-andrews.ac.uk
In many unconventional superconductors, magnetism and superconductivity occur in close proximity to each other - which is surprising given that they are usually considered mutually exclusive properties of a material. This is also true for the iron pnictide superconductors, where in several materials magnetism and superconductivity appear to coexist from macroscopic measurements. In this project, you will take an atomic scale view at the magnetic order and the superconducting properties using low temperature spin-polarized scanning tunneling microscopy[1]. Combining images of the magnetic order with a characterization of superconductivity from tunneling spectroscopy will allow to establish whether magnetism and superconductivity coexist microscopically, or whether they are really competing. These results provide important benchmarks for theory, and may help to establish an understanding of superconductivity in these materials.
You will be using bespoke low temperature scanning tunneling microscopes, which are installed in a new ultra-low-vibration facility at the University of St Andrews.
[1] Enayat et al., Science 345, 653 (2014).
Tunneling Spectroscopy of Strongly Correlated Electron Materials
Quantum Critical Points in Ferroelectrics
Scott, Prof Jim - jfs4@st-andrews.ac.uk
When crystals undergo phase transitions at or near zero degrees Kelvin their dynamics differ from those at higher temperatures. Entropy is still involved but arises from quantum mechanical uncertainty, rather than classical effects; this mixes together spatial and temporal fluctuations. Most systems studied thus far involve ferromagnetism or superconductivity, but some work [1,2] has been done by Scott on ferroelectrics. In a pseudo-cubic structure such as SrTiO3 or KTaO3 the main effect is that the isothermal electric susceptibility (dielectric constant) varies as 1/T-squared, rather than the classic Curie-Weiss 1/T, and the effective dimensionality is d+1 = 4. But in highly uniaxial materials, the effective dimensionality is d+1 = 5, which results in the dielectric constant varying exactly as 1/T-cubed [3].
We have recently demonstrated that in the uniaxial materials BaFe12O19, SrFe12O19, and PbFe(12-x)Ga(x)O3. The Ba-isomorph is the most profitable magnetic material in Nature, with �2 billion in sales every year (a few grams for every person on Earth!), primarily as the magnetic stripe material for credit cards. Therefore, although this project is unapplied, it is related to device materials of great commercial interest.
[1] S. E. Rowley et al., Nature Physics (2014)
[2] S. E. Rowley et al., arXiv condmat (2014)
[3] D. Khmelnitskii, JETP Lett. (2014)
The thesis work will not involve growing crystals (they are already in hand) nor building a lab; most of the kit is already operational in Dr. F. Morrison's lab in the School of Chemistry. However, a relatively sophisticated level of data analysis and modelling will be encouraged. Therefore although the project is experimental, students with a high level of interest in theory might find it attractive.
It is probable that summer salary would be available for a PhD student wishing to begin in June or July.
Room-temperature Multiferroics
Multiferroics are usually defined as crystals that are simultaneously ferromagnetic and ferroelectric. Most are also magnetoelectric, meaning that their magnetization M can be switched by applied electric field and their polarization P switched via applied magnetic field H.
This PhD thesis project will emphasize the materials GaFeO3 and its isomorphs, as well as PbFe(1/2)Nb(1/2)O3 and related Ta, Ti, and Nb compounds.
The thesis work will not involve growing crystals (they are already in hand) nor building a lab; most of the kit is already operational in Dr. F. Morrison's lab in the School of Chemistry. However, a rewlatively sophisticated level of data analysis and modelling will be encouraged. Therefore although the project is experimental, students with a high level of interest in theory might find it attractive.
Superconductivity in Non-Centrosymmetric Materials and Structures
The aim of this project is to investigate experimentally the influence of broken inversion symmetry on superconductivity in a variety of non-centrosymmetric (NCS) materials.
Most crystalline metals have a structure that maps onto itself exactly under inversion of spatial coordinates. Such materials are termed �centrosymmetric� and when they become superconducting, the spatial part of the Cooper pair wavefunction must have a definite parity, i.e. inversion simply multiplies it by �1. This imposes restrictions also on the spin configuration within the Cooper pair. By contrast, in non-centrosymmetric superconductors where the crystal structure breaks inversion symmetry, such restrictions do not apply. Amongst the properties predicted for non-centrosymmetric superconductors are mixed spin-singlet/spin-triplet pairing, enhanced critical fields and spatially modulated superconducting states. Whilst unusual superconducting properties have been detected in a number of NCS materials, there is relatively little firm experimental evidence linking these to the lack of inversion symmetry; for example only in very few cases has a substantial triplet component of the order parameter been firmly established.
The project will be focused on NCS superconductors where the electronic correlations are weak, since these offer the chance to isolate the role of the broken inversion symmetry. The experiments will focus on using low temperature scanning tunneling microscopy and spectroscopy to establish the structure of the superconducting order parameter and study the influence of defects of different dimensionalities on the superconducting properties.
2D Quantum Materials
King, Prof Phil - pdk6@st-andrews.ac.uk
As part of a generously-funded research project from the Leverhulme Trust, we are seeking ambitious and motivated PhD students to join a major research initiative aimed at investigating the electronic structure and collective states of two-dimensional quantum materials. The remarkable properties of graphene, a single atom-thick layer of carbon, has spurred enormous interest in 2D materials. In this project, you will seek to develop 2D material systems which incorporate the effects of pronounced electronic interactions, focusing on transition-metal dichalcogenide (TMD) compounds. Bulk TMDs are known to support a wide variety of striking physical properties such as superconductivity and charge density-wave states, but how these are modified when the material is restricted to just a single layer in thickness are only starting to be explored. Combining strongly-interacting 2D materials in different configurations and environments promises a huge array of exciting possibilities to stabilise rich phase diagrams and unique properties. The work undertaken will build on the group�s existing activity in the study of bulk and monolayer TMDs [e.g. 1-5], and ultimately aims to develop new routes towards the �on-demand� control of the quantum many-body system underpinning the physical properties of 2D quantum materials. Projects are available developing the growth of single monolayers and heterostructures of TMD compounds using a recently-installed state-of-the art molecular-beam epitaxy system in St Andrews and utilizing a linked system for angle-resolved photoemission spectroscopy, as well as further ARPES and spin-resolved ARPES work at international synchrotrons, to probe the resulting electronic structure and many-body interactions of the materials synthesized. There are also possibilities to spend extended research visits with our collaborators in Tokyo and in Italy. As part of this project, you will undertake experiments at national and international facilities. Thus, a willingness to travel is an essential prerequisite. For further information, or to discuss specific research possibilities, please contact philip.king@st-andrews.ac.uk.
[1] Riley et al., Nature Physics 10 (2014) 835
[2] Riley et al., Nature Nano. 10 (2015) 1043
[3] Bawden et al., Nature Commun. 7 (2015) 11711
[4] Bahramy, Clark et al., Nature Materials, 17 (2018) 21
[5] Feng et al., Nano Lett. 18 (2018) 4493
ARPES on correlated materials
Ambient pressure photoemission spectroscopy of organic semiconductor devices
Turnbull, Prof Graham - gat@st-andrews.ac.uk
Ambient pressure photoemission spectroscopy is a new technique to measure the energy levels of materials. Combined with scanning Kelvin probe spectroscopy APS can provide information about the electronic properties of thin film materials relevant to LEDs, solar cells, sensors and lasers. The aim of this project will be to combine measurements of the energy levels of organic semiconductors to understand their operation in optoelectronic devices.
The HOMO and LUMO levels of organic semiconductors are crucial to charge injection, exciton formation, energy transfer and charge transfer in OLEDs, solar cells, lasers and chemical sensors. Currently the standard measurement to determine energy levels is cyclic voltammetry but this is typically used to measure individual molecules in solution, and there would be a lot of advantage if we could measure directly the materials int he solid-state including thin films as used in devices.
Applications of these measurements would be to better understand the operation of solar cells, OLEDs and thin film chemical sensors.
Organic Photonics
Artificial quantum materials
The epitaxial compatibility of many oxides which, in bulk form, host an extraordinarily wide array of physical properties opens almost limitless possibilities for creating new artificial materials structured at the atomic scale [1]. Recent advances in atomically-precise deposition techniques have opened new potential to manipulate the properties of these ubiquitous but still poorly-understood materials [2], creating new "designer" compounds with tailored properties not found in bulk. You will exploit a brand new �1.8M growth facility to build up transition-metal oxide materials one atomic layer at a time, exploiting tuning parameters such as epitaxial strain and the layering of disparate compounds to selectively tune their functional properties. To provide direct feedback on how this influences the underlying quantum states in these complex materials, you will employ advanced spectroscopic probes such as angle-resolved photoemission [3] or scanning tunneling microscopy and spectroscopy [4], utilizing our state-of-the-art capabilities in St Andrews. Together, this promises new insight into the rational design of quantum materials and their potential for future quantum technologies.
[1] J. Mannhart and D. Schlom, Science 327, 1607 (2010).
[2] P.D.C. King et al., Nature Nano. 9, 443 (2014).
[3] V. Sunko et al., Nature 549, 492 (2017).
[4] M. Enayat et al., Science 345, 653 (2014).
Artificial Quantum Materials - Thermodynamics And Transport
Rost, Dr Andreas - ar35@st-andrews.ac.uk
Artificial designer heterostructures of correlated electron systems open up a wide range of exciting possibilities for the creation of new materials. The atomic-layer-by-atomic-layer deposition now achievable in thin films gives a unique potential to manipulate the properties of this still poorly explored new class of materials, ultimately allowing the creation of new phases with properties difficult to attain in bulk compounds [1]. St Andrews has recently opened a new dedicated MBE growth facility with the aim of exploiting the possibilities of such tailored materials.
This new class of materials, however, poses a key challenge to experimentalists interested in such basic thermodynamic properties as specific heat and magnetisation. The extremely low �thermal mass� of such materials compared to bulk systems ultimately requires the development of a new bespoke set of experimental tools for measurement. To bring the paradigm of such fundamental thermodynamic measurements to nanoscale thin films is the key aim of a new research program established at the University of St Andrews of which you will be a key member. During your PhD you will contribute to the development of these new tools with the aim to applying them to the study of designer quantum materials spanning phenomena such as superconductivity, novel (topological) Dirac- and Weyl- systems and (quantum) spin liquids.
Atomic-scale imaging of complex magnetic orders in quantum materials
Many quantum materials exhibit complex magnetic orders, which often are sensitive to external stimuli, such as magnetic field or doping, making them in principle interesting for many technological applications. Characterization of the spatial structure of the magnetic order has mostly been done through Neutron scattering, which however average over a macroscopic sample volume. Spin-polarized scanning tunneling microscope provides real space images of magnetic order at the atomic scale, thereby providing new insights into the spatial structure of the complex magnetic orders. In this project, you will use low temperature scanning tunneling microscopy in a vector magnetic field to characterize the magnetic structure of quantum materials. The studies will aim to establish the surface impact on the magnetic order, knowledge which is critical for technological exploitation and interfacing to other materials, but also to provide a microscopic picture of the magnetic order which will help to identify the dominant contributions to the magnetic interactions in the material. We are in particular interested in metamagnetic phases, where the external magnetic fields can drive phase transitions in the material.
[2] Singh et al., Phys. Rev. B 91, 161111 (2015).
[3] Trainer, et al., Rev. Sci. Instr. 88, 093705 (2017).
Coherent many-body dynamics between a quantum system and its environment
Braunecker, Dr Bernd - bhb@st-andrews.ac.uk
Decoherence, the enemy of any quantum processing, is the uncontrolled decay of a well defined quantum superposition. It occurs because any quantum system is always embedded in a wider environment with a macroscopic number of degrees of freedom. The interaction with these degrees of freedom causes a destructive interference and a nicely prepared quantum superposition dissipates somewhere in the environment. Large efforts are thus made throughout the world to isolate the system from its environment, to use special driving protocols that reverse some of the destructive interference, etc.
However, the concept of "bad" can also be reversed into something "good". It is indeed interesting to ask how exactly decoherence builds up, if we can use this to learn something about the system and the environment, and even if there is a way to use this knowledge for quantum information processing. Indeed the quantum fluctuations that eventually turn into decoherence initially build up an entanglement with the environment. The main questions underlying this PhD project are how this happens, how it can be followed in time, and if we can use it in a controlled way.
As a first example we have worked out in detail how a spin decays in a metal [1]. The stationary properties of such a system are known since very long and the analysis of the thermal decay is on the basis of magnetic resonance techniques such as NMR or MRI. However, mostly left aside was the regime of very short time scales in which the spin and a part of the metallic environment have a joint coherent evolution, and in which coherent excitations in the metal act back on the spin dynamics. The coherent many-body effect of a local excitation, such as from a spin flip, on the environment runs under the name of orthogonality catastrophe or Fermi edge singularity, is on the basis of the Kondo effect, and we have worked on extending the techniques to access this physics for various situations over many years. In [1] we have now set up the approach allowing us to systematically investigate the backaction on the spin as well. This proposed PhD work will build on these foundations and make the transition to including strongly correlated many-body environments. The goal is to provide a framework for the characterisation of correlated systems through probing localised spins, which is de facto an extension of the foundations of NMR to strongly interacting systems in which temporal correlations are as important as the spatial correlations that alone are addressed in current theories. Through the tremendous progress made in material design, low temperature physics and quantum control such a theoretical foundation is becoming more and more necessary.
[1] S. Matern, D. Loss, J. Klinovaja, B. Braunecker, Phys. Rev. B 100, 134308 (2019) [arXiv:1905.11422]
Theory of Condensed Matter - BHB
Controlling emergent quantum phases through strain-tuning of electronic structure
Hicks , Dr Clifford - cwh10@st-andrews.ac.uk
Mackenzie, Prof Andy - apm9@st-andrews.ac.uk
The strong interactions at the heart of correlated electron materials yield striking collective states such as superconductivity or magnetism, and often mediate giant responses to small external perturbations. This offers unique opportunities to tune these subtle quantum many-body systems, to shed new light on their underlying physics and ultimately to engineer desired functional properties. In this project, you will exploit externally-applied and continuously-tunable mechanical strain in an attempt to harness control over emergent phases in correlated solids, for example tuning unconventional superconductivity in Sr2RuO4 and controlling quantum criticality in Sr3Ru2O7. You will perform low-temperature transport measurements as a function of uni- and bi-axial strain using custom apparatus within the world-leading facilities of the Max-Planck Institute for the Chemical Physics of Solids in Dresden, Germany. You will also design similar apparatus that can be integrated within our state-of-the-art system for angle-resolved photoemission (ARPES) in St Andrews, as well as in ARPES systems at synchrotron light sources. This will allow you to track the corresponding electronic structure changes that control the materials� transport and thermodynamic properties with unprecedented detail. This project is offered as part of a Max Planck � CM-DTC initiative (http://cm-dtc.supa.ac.uk/research/max%20planck.php). You will spend part of your time performing research in MPI Dresden (with Dr. Hicks & Prof. Mackenzie), part in St Andrews (with Prof. King), and will also undertake experiments at national and international facilities. Thus, a willingness to travel is an essential prerequisite.
Correlated Electron Systems
Dynamical Coulomb blockade in arbitrary environments with backaction
Quantum simulation offers the possibility to create physical phenomena that are hard to access or control otherwise. Notorious is particularly many-body physics with strong correlations. Remarkably some types of such physics can be created in dissipative quantum circuits, in which the type of correlation physics appears through a nonlinear interaction of the electron transport with electromagnetic environment fluctuations. For weakly transmitting conductor such physics is understood since a long time [1]. But the potential of the quantum simulation appears only for highly transmitting circuits in which the transmission time is comparable with the environment's reaction time, called the dynamical Coulomb blockade regime, for which much less is known. Although for specific conditions important advances have been made over the last years [2], recent experimental progress has shown that there is still much unclear especially when there is strong backaction of the environment [3]. In this PhD project we will access this physics through analytical and numerical non-perturbative many-body modelling, including bosonisation [4] and recently developed mappings on scattering boundary value problems [5].
[1] G.-L. Ingold and Y. Nazarov, in Single Charge Tunneling ed. by H. Grabert and M. H. Devoret, Ch. 2 (Plenum, 1992).
[2] K. A. Matveev, D. Yue and L. I. Glazman, Phys. Rev. Lett. 71, 3351 (1993); L. W. K. Molenkamp, Flensberg and M. Kemerink, Phys. Rev. Lett. 75, 4282 (1995). Y. V. Nazarov, Phys. Rev. Lett. 82, 1245 (1999); M. Kindermann and Y. V. Nazarov, Phys. Rev. Lett. 91, 136802 (2003); I. Safi and H. Saleur, Phys. Rev. Lett. 93, 126602 (2004); D. S. Golubev, A. V., Galaktionov and A. D. Zaikin, Phys. Rev. B 72, 205417 (2005).
[3] F. D. Parmentier, A. Anthore, S. Jezouin, H. le Sueur, U. Gennser, A. Cavanna, D. Mailly and F. Pierre, Nat. Phys. 7, 935 (2011); A. Anthore, Z. Iftikhar, E. Boulat, F. D. Parmentier, A. Cavanna, A. Ouerghi, U. Gennser, and F. Pierre, Phys. Rev. X 8, 031075 (2018).
[4] J.-R. Souquet, I. Safi, and P. Simon, Phys. Rev. B 88, 205419 (2013).
[5] B. A. Muzykantskii and Y. Adamov, Phys. Rev. B 68, 155304 (2003); B. Muzykantskii, N. d'Ambrumenil, and B. Braunecker, Phys. Rev. Lett. 91, 266602 (2003); J. Zhang, Y. Sherkunov, N. d'Ambrumenil, and B. Muzykantskii, Phys. Rev. B 80, 245308 (2009); B. Braunecker, Phys. Rev. B. 73, 075122 (2006).
Electron transport through molecules: A new kind of open quantum system theory (with Dr Erik Gauger, Heriot Watt)
Lovett, Dr Brendon - bwl4@st-andrews.ac.uk
Controlling how electrons flow through molecular structures is key to designing future miniaturised electronic components [1]. Understanding and manipulating such charge transport is a very challenging problem at this nanoscopic scale, especially in the common situation of strong interactions between the charges carriers and the vibrational mode structure of the environment [2]. In this project, you will develop such an understanding using advanced techniques for simulating open quantum systems.
We have recently developed a groundbreaking new theoretical method [3] which relies on a combination of Feynman path integrals and matrix product states, and which opens up the possibility of a multitude of new calculations. The tool that you will develop will be a significant adaptation of this new method, and will describe any quantum problem in which a small system is coupled to both bosonic and fermionic environments.
We hope to reveal new insights into how electron currents in molecules behave, and this will allow us to design new molecular devices that exploit quantum coherence.
[1] S. V. Aradhya and L. Venkataraman, Nat. Nanotechnol. 8 399 (2013).
[2] J. Sowa, J. A. Mol, G. A. D. Briggs, and E. M. Gauger, The Journal of Chemical Physics 149, 154112 (2018)
[3] A. Strathearn, P. Kirton, D. Kilda, J. Keeling, and B. W. Lovett, Nature Communications 9 3322 (2018)
Theory of Quantum Nanomaterials
Engineering non-equilibrium material states with cold atoms in optical cavities
Keeling, Dr Jonathan - jmjk@st-andrews.ac.uk
A triumph of 20th century condensed matter physics is the understanding of the phases of matter, arising from interacting many body problems in thermal equilibrium. However, not all matter is in equilibrium, and the understanding of matter out of equilibrium is far less developed. To develop our understanding of this, it is necessary both to develop new theoretical techniques, and to identify clean experimental systems where these approaches can be tested against known problems.
Ultracold atoms have provided an excellent testbed for simulating canonical models in equilibrium, and can be adapted to probe non-equilibrium physics. In particular, ultracold atoms placed in optical cavities can be used to prepare and control non-equilibrium states of matter. Specifically, these experiments involve driving by scattering a pump laser into the optical cavity, leading to cavity mediated interactions between atoms, accompanied with collective dissipation processes. While experiments on atoms single mode cavities have been studied extensively, experiments on multimode cavities are only just beginning. These have the potential to transform the kinds of behaviour one can study.
Our theoretical group collaborates closely with the experimental group of Benjamin Lev (Stanford) who have built a multimode optical cavity[1,2], and are now in the position to use this to explore novel states of matter. Several ideas in this direction have been proposed[3,4,5], including liquid crystaline phases of matter[3], spin glass states [4] and Hopfiled associative memories[5]. However, understanding of the non-equilibrium nature of these phases is yet unclear.
This PhD will explore a number of these topics; we will work in close collaboration with the Lev group in Stanford, so the precise projects will be determined in order to match ongoing and future experiments. We will make use of a variety of analytical and numerical techniques, potentially including matrix product state calculations.
[1] "Tunable-Range, Photon-Mediated Atomic Interactions in Multimode Cavity QED", V. D. Vaidya, Y. Guo, R. M. Kroeze, K. E. Ballantine, A. J. Kollar, J. Keeling, and B. L. Lev, Phys. Rev. X 8 011002 (2018)
[2] "Sinor self-ordering of a quantum gas in a cavity." R. M. Kroeze, Y. Guo, V. D. Vaidya, J. Keeling, B. L. Lev arXiv:1807.04915
[3] "Emergent Crystallinity and Frustration with Bose-Einstein Condensates in Multimode Cavities", S. Gopalakrishnan, B. L. Lev, and P. M. Goldbart, Nat. Phys. 5, 845 (2009).
[4] "Frustration and Glassiness in Spin Models with Cavity-Mediated Interactions." S. Gopalakrishnan, B. L. Lev, and P. M. Goldbart, Phys. Rev. Lett. 107, 277201 (2011).
[5] "Exploring Models of Associative Memory via Cavity Quantum Electrodynamics", S. Gopalakrishnan, B. L. Lev, and P. M. Goldbart, Philos. Mag. 92, 353 (2012).
Theory of Condensed Matter - JMJK
Exciton Diffusion in Organic Semiconductors
Samuel, Prof Ifor - idws@st-andrews.ac.uk
The discovery of semiconducting properties in organic materials has opened major new directions in semiconductor physics. Organic semiconductors combine the simple fabrication and tuning of properties that is typical of plastics with novel optoelectronic properties useful for devices such as light-emitting diodes and solar cells. The low-dimensional nature of these materials means that excitons (electron-hole pairs) are strongly bound even at room temperature and play a very important role in their physics. Whilst charge transport has been widely studied, exciton transport has been largely overlooked. We have now developed techniques based on time-resolved spectroscopy that allow the measurement of exciton diffusion. We now wish to apply them to understand the physics of exciton diffusion and the factors controlling it. A breakthrough in this field could in turn lead to a breakthrough in the efficiency of organic solar cells.
Organic semiconductor centre
Experimental and Theoretical Investigation of Spatially Modulated Magnetic Phases Near to Quantum Criticality
Huxley, Prof Andrew - ah311@st-andrews.ac.uk
The possibility of magnetic spin-crystals formed by the superposition of helical spin modulations with different wave-vectors has been a subject of much recent experimental and theoretical work. Signatures of phases with this property have been found in an array of materials including MnSi and Sr3Ru2O7. On the theoretical side, there are several ways in which such states might form. These include the formation of spiral modulation due to a Dzyalosinskii-Moriya spin-orbit interaction in itinerant magnets, residual, small-wavevector nesting due to the electron dispersion in a lattice [1,2] and from competing interactions that can give rise to a series of transitions forming a Devil's Staircase [3]. Perhaps the most intriguing suggestion - and one that has most captured the imagination of condensed matter theorists of late - is that an itinerant system on the brink of a quantum phase transition might possess an intrinsic instability to the formation of modulated magnetic phases [4]. In any particular material, one or more of these effects may operate with the possibility of a complicated interplay between them.
This project aims to investigate the phenomenon of spatially modulated magnetism from both an experimental and theoretical perspective. We will use techniques of quantum many-body physics and field theory to investigate the possibility of spatially modulated magnetism in real systems. These investigations will be carried out in concert with neutron scattering experiments to provide inspiration for and validate this theory. The experimental part will include growing the crystals for these experiments as well as performing the measurements. We anticipate that a student will spend approximately 2/3 of their time on theory and 1/3 on experimental work, working both in Edinburgh and St Andrews as well as at international facilities.
[1] A. M. Berridge, A. G. Green, S. A. Grigera and B. D. Simons "A Magnetic Analogue of the of the FFLO state: Inhomogeneous Instabilities Near to Tricritical Points" Physical Review Letters 102, 149903 (2009).
[2] G. J. Conduit, A. G. Green, and B. D. Simons, "Inhomogeneous phase formation on the border of itinerant ferromagnetism" Physical Review Letters 103, 207201 (2009) [spotlighted in Physics 2, 93 (2009)]
[3] P. Bak & J. von Boehm, "Ising model with solitons, phasons, and 'the devil's staircase'", Phys Rev B 21 5297 (1980)
[4] J. Rech C.P�pin, V.Chubukov, "Quantum critical behaviour in intinerant electron systems: Eliashberg theory and instability of a ferromagentic quantum critical point" Phys Rev B 74 195126 (2006)
Quantum order at extreme conditions
Fidelity plateaux from correlated noise: beyond the two-state case
Hooley, Dr Chris - cah19@st-andrews.ac.uk
When disorder is studied in the solid state, it is usually considered to be independent of time, and to affect only one parameter of the Hamiltonian (e.g. the on-site energy or the nearest-neighbour hopping amplitude). In the cold-atom context, neither of these assumptions is likely to hold. Disorder will generally be time-dependent, arising for example from the failure of the laser controller to achieve some desired ramp profile. It will also generally appear in a correlated way in multiple parameters of the Hamiltonian.
CM-CDT student Scott Taylor and I have recently shown [1] that this leads to a striking effect, viz. the occurrence of arbitrarily long plateaux in the state-preparation fidelity. However, our work so far has dealt only with the simplest case of a driven two-level system.
The aim of this project is to study the effects of correlated time-dependent disorder in a broader range of Hamiltonians, especially those with a Hilbert space of dimension greater than two. In particular, it aims to connect the abovementioned observation with the phenomenon of many-body localisation [2] and the new phases of matter possible in driven non-equilibrium quantum systems [3].
[1] S.R. Taylor and C.A. Hooley, arXiv:1711.05131 (2017).
[2] R. Nandkishore and D.A. Huse, Annu. Rev. Cond. Matt. Phys. 6, 15 (2015).
[3] F. Harper and R. Roy, Phys. Rev. Lett. 118, 115301 (2017).
Category: Theoretical Hard Condensed Matter
Theory of Condensed Matter - CAH
Finite-temperature behaviour of quantum Kasteleyn systems
Recent work on the so-called �spin ice� materials [1] has produced a resurgence of interest in Kasteleyn transitions [2]. In a typical demagnetisation transition, the magnetism of a sample is reduced by the formation of local domains of flipped spins. In a Kasteleyn transition, however, these are effectively forbidden, and the transition is driven instead by the appearance of lines of flipped spins that extend all the way from one side of the sample to the other.
The standard theory of these transitions is purely classical, with the transition being driven by increasing temperature. But it is interesting to ask whether there is a quantum version of such a transition, driven by (for example) a transverse magnetic field [3]. If so, it should give rise to interesting finite-temperature phenomena: the Kasteleyn analogues of the quantum criticality observed in the conventional case [4].
The initial goal of this project is to determine whether a quantum Kasteleyn transition exists in a particular toy model [3], and then to develop a theory of the finite-temperature behaviour of the model in the vicinity of the quantum Kasteleyn point.
[1] C. Castelnovo, R. Moessner, and S.L. Sondhi, Nature 451, 42 (2008).
[2] L.D.C. Jaubert, J.T. Chalker, P.C.W. Holdsworth, and R. Moessner, Phys. Rev. Lett. 100, 067207 (2008).
[3] S.A. Grigera and C.A. Hooley, arXiv:1607.04657.
[4] S. Chakravarty, B.I. Halperin, and D.R. Nelson, Phys. Rev. B 39, 2344 (1989).
Holographic traps and guides for superfluidity studies and atom interferometry
Cassettari, Dr Donatella - dc43@st-andrews.ac.uk
Holographic traps are a new kind of optical traps for neutral atoms which are promising for a wide range of applications, e.g. quantum information processing and quantum simulation. They are produced by diffracting a laser beam off a computer-controlled optical device, known as a Spatial Light Modulator (SLM). This apparatus offers unparalleled flexibility in the choice of trapping geometry, and different experiments can be done simply by reconfiguring the SLM.
In this PhD project you will work on:
- Double well traps for confined atom interferometry, which is promising for the development of sensitive devices (see [1] for a review).
- Ring-shaped atom guides (see [2] and [3]), which can be used to observe superfluid motion of a Bose-Einstein condensate, e.g. persistent current states. BECs in these geometries and the study of their critical velocities (where superflow stops) have very important technological applications in sensing devices, such as superconducting quantum interference devices (SQUIDs). Moreover, theoretical proposals have been put forward in which coherent superposition of different BEC flows can be used as qubits.
[1] http://rmp.aps.org/abstract/RMP/v81/i3/p1051_1
[2] http://prl.aps.org/abstract/PRL/v106/i13/e130401
[3] http://lanl.arxiv.org/abs/1008.2140
Holographic traps for the efficient production of Bose-Einstein condensates
Evaporative cooling is an essential stage in the creation of Bose-Einstein condensates (BECs) in atomic gases. Recently we suggested [1] that holographic optical traps can be used to increase the evaporation efficiency, leading to larger BECs. In this PhD project you will implement this scheme, which will result in a simplified apparatus for the productions and subsequent manipulation of BECs.
[1] http://pra.aps.org/abstract/PRA/v84/i5/e053410
Investigating novel superconducting ground states in nanofabricated hybrid ferromagnetic-superconducting materials and devices using advanced neutron, muon and synchrotron techniques
Lee, Prof Steve - sl10@st-andrews.ac.uk
The search for novel quantum states of matter in artificial thin-film structures, in which superconducting (S) and ferromagnetic (F) materials are juxtaposed, has reached an exciting and timely stage of development. In the last year a series of new landmark experimental results seem set to herald a period of rapid expansion of interest and activity in the field. This was the pioneering observation by several groups of spin-triplet supercurrents traversing relatively thick F layers [1-3], believed theoretically to be signatures of a novel equal-spin spin-triplet and possibly �odd frequency� superconducting state. This achievement represent the culmination of several years of breakthrough experiments [1-7] in a field whose modern era began almost most a decade ago, with the experimental discovery of Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) [8] type states in S-F-S structures [10]. What both the FFLO [8] and the odd-frequency pairing phenomena [9] have in common is that they were predicted to occur theoretically in bulk systems [8,9] but only in state-of-the-art artificial thin-film structures were they finally demonstrated to exist [1-7,10-13]. Modern thin-film growth and large area lithographic patterning open-up an enormous range of further possibilities for engendering novel quantum states of matter via the controlled interaction S and F order on the nanoscale. This capability also offers the promise of designing and engineering hybrid metamaterials (in a similar spirit to electromagnetic metamaterials) with tailored quantum properties. Concurrently there is enormous interest in spintronics, the manipulation of electronic spin for application in novel electronic devices. The structures investigated within this programme marry the fields of mesoscopic superconductivity, novel strongly correlated electron physics and spintronics. By introducing quantum coherence phenomena into spintronic types devices, this also opens up the possibility of non-locality and entanglement, with possible application long-term in quantum computation.
Professor Steve Lee leads an EPSRC funded Critical Mass Grant award (St Andrews, Leeds, Bath, Royal Holloway, ISIS, with partners in PSI ( Swizterland), Cambridge, and Leiden ) that underpins an international research programme that brings together a team with a wide range of relevant expertise to explore the physics of such systems. We make use of some of the most powerful probes in condensed matter physics (scattering and surface probe techniques) in order to throw new light onto the physics of artificial S-F metamaterials, with particular emphasis on spatially�resolved measurements. This combines with state-of-the-art facilities for materials growth and patterning and world leading instrumentation for measurement. The programme is also informed by cutting-edge theory. There are significant opportunities for research students within this collaboration, with excellent access to world leading research facilities (such as Diamond, ISIS, ILL, PSI, SLS). Due to the strong interactions between nodes there is also significant scope for student mobility in order to enhance training and experience. This is all underpinned by access to excellent graduate training bot via the SUPA Graduate School and the additional benefits of the Doctoral Training Centre in condensed matter physics based at St Andrews, Edinburgh and Heriot Watt.
[1] J.W.A. Robinson et al., Science 329 59 (2010).
[2] T.S. Khaire et al., PRL 104, 137002 (2010).
[3] M.S. Anwar et al., PRB 82, 100501 (2010).
[4] R.S. Keizer et al., Nature 439 825 (2006).
[5] J. Wang et al., Nat. Phys. 6 389 (2010).
[6] I. Sosnin et al., PRL 96 157002 (2006).
[7] D. Sprungmann et al., PRB 82, 060505 (2010).
[8] P. Fulde and R.A. Ferrell, PRB 135 A550 (1964);
A.I. Larkin and Y.N. Ovchinnikov, Zh. Eksp.
Teor. Fiz. 47, 1136 (1964).
[9] V.L. Berezinskii, JEPT Lett. 20, 287 (1974).
[10] V.V. Ryazanov et al., PRL 86, 2427 (2001); T. Kontos et al., PRL 89, 137007 (2002).
[11] A.I. Buzdin et al., JETP Letters 35, 178 (1982);
[12] F.S. Bergeret et al., PRL 86, 4096 (2001); Rev. Mod. Phys. 77, 1321 (2005).
[13] M. Eschrig et al., PRL 90, 137003 (2003); M. Eschrig and T. L�fwander, Nature Phys. 4 138 (2008).
Superconductivity and Magnetism
Local control and manipulation of electronic properties of transition metal oxide surfaces
Transition metal oxides host a wide range of physical properties and functionalities, making them an ideal platform for implementing potential future devices. The aim of this project is to establish novel ways to manipulate the local properties of transition metal oxides by using a scanning tunneling microscope to enable writing device structures at the atomic scale into the surface of the material. To establish the properties of these written device structure, you will first use scanning tunneling spectroscopy, but later also explore possibilities to contact the written structures macroscopically to study transport through these and enable actual device operation.
While initial studies will be performed on bulk material, at later stages of the project, thin-film samples grown by reactive oxide molecular beam epitaxy will be used.
Mesoscopic unconventional superconductors and Fermi liquids
This project is offer in conjunction with Prof. Amir Yacoby at Harvard.
In this project, we aim to bridge the gap between two fields in which huge progress has been made over the past twenty years. In mesoscopic physics, the aim is to work with samples that are specially fabricated so that their physical size becomes comparable with one or more of the fundamental length scales of the underlying physics. In a metal this might be the mean free path, and in a superconductor it might be the coherence length or the penetration depth. So far, the vast majority of research into mesoscopic physics has been performed on traditional materials in which the electron-electron interactions are relatively weak. In parallel with these developments, equally rapid progress has been made on research into new materials with very strong electron-electron interactions, which lead to high quasiparticle masses and an exciting variety of metallic, superconducting and magnetic ground states. For technical reasons the two fields have advanced in parallel, with little cross-fertilisation of ideas and techniques. The goal of this jointly supervised project is to combine the different expertise of our two groups to bring strongly interacting electrons into the mesoscopic regime. You will work both in St Andrews and at the spectacular new Harvard Nanoscience Center, performing pioneering experiments on the fabrication and measurement of correlated electron mesoscopic devices.
(Jointly affiliated to both University of St Andrews and Max Planck Institute for the Chemical Physics of Solids, Dresden)
Novel Quantum Order in Vector Magnetic Fields
Strongly interacting electron systems are one of the best hosts for study of the quantum many-body problem. Experimental discoveries made in the past decade show that, in the cleanest materials, a variety of subtle collective states form at low temperatures. Some of these are metallic but involve the development of a preferred direction, driven not by the crystal symmetry but by the electron-electron interactions themselves. To study anisotropic responses like these, careful experiments are necessary � they can easily be missed if the correct probes are not used. Many of the states discovered so far have a coupling to externally applied magnetic fields, so these fields can be used to �train� the systems� response functions. This has highlighted the need to develop better and better �vector magnets� in which the field vector can be changed via computer-controlled energisation of multiple superconducting coils. On this project you will have access to world-leading instruments capable of generating 1, 1 and 9 tesla along the x, y and z axes. This will enable you to study transport and thermodynamic quantities that cannot be accessed in standard instruments. Using this unique instrumentation, you will have the chance to investigate a range of the most exciting new strongly correlated materials in a fast-moving field of modern research.
Path integrals over matrix product states: applications and extensions
The realisation that the ground states of short-range quantum spin systems can generically be represented by matrix product states is an important recent development in theoretical physics [1]. With the aim of integrating the insights of matrix product states with the powerful tools of quantum field theory, some colleagues and I recently developed a path integral over one-dimensional versions of such states [2].
The aim of this project is threefold: first, to explore the extension of this matrix-product-state path integral to higher-dimensional systems; second, to investigate the nature and physical meaning of instanton processes in such path integrals; and third, to develop further applications of the matrix-product-state path integral to open questions in the physics of frustrated magnetism.
[1] R. Or�s, Ann. Phys. 349, 117 (2014).
[2] A.G. Green, C.A. Hooley, J. Keeling, and S.H. Simon, arXiv:1607.01778 (2016).
Polaritons in organic semiconductor microcavities
When light is confined on the nanoscale it is possible to observe light-matter interactions that are not normally observed in bulk materials. One example is the strong coupling of photons and excitons in wavelength-scale microcavities which leads to a number of unusual phenomena [1,2]. The modes of the cavity couple with the exciton to make a hybrid-light-matter state called a polariton. One can make polaritons lasers that emit coherent light [3] and it has been shown that polaritons can form a Bose-Einstein condenstate [4].
This project will explore the properties of polaritons in microcavities based on organic semiconductors [2,4-6]. It will involve the fabrication of microcavities that include J-aggregate dyes or semiconducting polymers to explore how the energy states of organic materials can be modified when coupled to the cavity modes, and be applied in photonic devices including lasers and LEDs.
[1] C. Weisbuch et al., Phys. Rev. Lett. 69, 3314 (1992)
[2] D.G. Lidzey et al., Nature 395, 53 (1998)
[3] S. Christopoulos et al., Phys. Rev. Lett. 98, 126405 (2007)
[4] J D Plumhof, T St�ferle, L Mai, U Scherf & R F Mahrt, Nature Materials 13, 247�252 (2014)
[5] T. Schwartz, J. A. Hutchison, C. Genet, and T. W. Ebbesen, Phys. Rev. Lett. 106, 196405 �(2011)
[6] S K�na-Cohen*, S A. Maier and D D. C. Bradley, Advanced Optical Materials 1, 827�833, (2013)
Quantum Electronic States in Delafossite Oxides
As part of a generously-funded ERC research project, we are seeking ambitious and motivated PhD students to join a major research initiative aimed at investigating Quantum Electronic States in Delafossite Oxides (QUESTDO). One of the most active challenges of modern solid state physics and chemistry is harnessing the unique and varied physical properties of transition-metal oxides. While little-studied to date, initial work suggests that the delafossite oxide metals are a particularly rich member of this materials class. They exhibit a wide array of fascinating properties, from ultra-high conductivity [1,2] to unconventional magnetism [3], with the potential to host strongly spin-orbit coupled states at their surfaces and interfaces [4]. You will seek to understand, and control, the delicate interplay of frustrated triangular and honeycomb lattice geometries, interacting electrons, and effects of strong spin-orbit interactions in stabilising these. Projects are available: (i) utilizing laboratory-, laser-, and synchrotron-based angle-resolved photoemission to probe their intriguing bulk and surface electronic structures and many-body interactions; (ii) developing the epitaxial growth of delafossites by reactive-oxide molecular-beam epitaxy, using a state-of-the-art system recently installed in St Andrews; or (iii) working jointly between us and our research partners at the Max-Planck Institute for the Chemical Physics of Solids, Dresden, pursuing either single-crystal growth of new delafossites, or density-functional theory calculations of their electronic structures, combined with experimental studies in our group. For further information, or to discuss research possibilities, please contact philip.king@st-andrews.ac.uk. As part of this project, you will undertake experiments at national and international facilities. Thus, a willingness to travel is an essential prerequisite.
[1] Kushwaha et al., Science Advances 1 (2015) 1500692
[2] Moll et al., Science 351 (2016) 1061
[3] Ok et al., Phys. Rev. Lett. 111 (2013) 176405
[4] Sunko et al., Nature 549 (2017) 492
Self-sustained topological phases in quasi-1D and 2D structures
Topological quantum phases have risen to a very active field of research recently, triggered mostly by the realisation that "ordinary" semiconductor nanostructures can be fine tuned to exhibit topological properties which are very attractive for quantum information storing and processing. With the link to semiconductors a major step forward has been taken towards a quantum technological implementation of such states, yet to obtain robust and scalable quantum systems the requirement of fine tuning has to be dropped.
Self-sustained topological phases provide such stable and robust systems, and exhibit a multitude of fascinating new physical properties that emerge as an effect of strongly interacting particles in a condensed matter system. We have already demonstrated that such phases spontaneously appear in hybrid magneto-electronic systems in one dimension [1-5]. Yet in 1D the number of topological states is restricted, and to obtain more exotic topological states extensions to higher dimensions must be made. It is, however, mandatory to maintain then the 1D self-sustaining mechanisms to avoid producing only conventional phases [6].
In this PhD project, we will take a systematic approach towards such self-sustained topological phases by enhancing the complexity of the systems step by step while maintaining full control over the strongly correlated electron state. We will investigate the influence of the lattice structure (square, honeycomb, kagome), anisotropies and frustration, as well as the crucial renormalisation of the system properties by electron interactions.
[1] B. Braunecker, P. Simon, and D. Loss, Phys. Rev. Lett. 102, 116403 (2009) [arXiv:0808.1685]
[2] B. Braunecker, P. Simon, and D. Loss, Phys. Rev. B 80, 165119 (2009) [arXiv:0908.0904]
[3] B. Braunecker and P. Simon, Phys. Rev. Lett. 111, 147202 (2013) [arXiv:1307.2431]
[4] B. Braunecker and P. Simon, Phys. Rev. B 92, 241410(R) (2015) [arXiv:1510.06339]
[5] C. J. F. Carroll and B. Braunecker arXiv:1709.06093
[6] P. Simon, B. Braunecker, and D. Loss, Phys. Rev. B 77, 045108 (2008) [arXiv:0709.0164]
Strong light-matter coupling with Rydberg polaritons
Ohadi, Dr Hamid - ho35@st-andrews.ac.uk
Joint PhD studentship between Scotland and Australia
Dr Hamid Ohadi (University of St Andrews, UK) (ho35@st-andrews.ac.uk)
A/Prof Thomas Volz (Macquarie University, Sydney, Australia)
Exploiting the laws of quantum mechanics for the benefit of humanity in the so-called "second quantum revolution" is one of the key goals of 21st-century physics. Unlike the first quantum revolution, which simply made use of the wave-particle duality that quantum mechanics dictates, the second quantum revolution harnesses entanglement, superposition and quantum measurement for creating new technologies. Ultimately, the quantum correlations at the heart of these phenomena require strong interactions between individual quantum particles. Many different quantum systems are currently being explored for applications, and photons, the quantum particles of light, are one of the most promising candidates for applications such as quantum information processing and quantum sensing. While they are easy to create, manipulate and detect, their biggest drawback, however, is the lack of direct interactions in vacuum. Yet, photons can be made to interact by binding them to matter. Photons propagating in an optically active material can couple strongly to the excitations of that material to the point where the photon and the material are entangled and form new hybrid particles that are half-matter and half-light. These chimeres are called 'polaritons' and have been at the forefront of modern quantum photonics research for the past two decades. While many spectacular results have been demonstrated so far, the ideal single-photon non-linear system has not been found to date.
This project aims to take a big leap forward and study a new exciting contender for inducing strong photon-photon interactions in a semiconductor system. Very recently, polaritons formed from electron hole pairs, i.e. excitons, in traditional semiconductor GaAs have been demonstrated to exhibit non-classical correlations at the single quantum level [1,2]. However, these correlations are weak due to the relatively weak interactions between the GaAs excitons. There are several avenues to induce even stronger interactions but almost all of them involve excitonic states that have a much larger interaction radius than the ground state GaAs excitons. A particularly interesting class of excitons are Rydberg excitons that in analogy to the hydrogen atom correspond to highly-excited excitons with large principal quantum numbers (and large spatial extent). Cuprous Oxides are known to have stable bulk Rydberg excitons with principal quantum numbers beyond n=20. Spectroscopy experiments have revealed effects due to exceptionally strong exciton-exciton interactions [3]. However, to date no light-matter interface with a 2D cuprous oxide film has been formed. This project will address this open problem and unlock the potential of the cuprous oxide material to form strongly interaction Rydberg polaritons.
The cotutelle project within the St-Andrew-Macquarie partnership will be conducted in two steps: In the first step, the semiconductor devices will be fabricated at the University of St Andrews. There will be two types of devices, one that will consist of a 2-dimensional microcavity formed by two highly reflective mirrors encapsulating a cuprous oxide thin film and a second type which is missing one of the mirrors and can be combined with an external mirror to form a fully-tunable system. Photons confined in the microcavity will strongly couple to the Rydberg excitons in the cuprous oxide film to form Rydberg polaritons. The second part of the project will be carried out at Macquarie University in Sydney. There the properties of the cuprous oxide polariton system will be explored with the expectation to demonstrate strong quantum correlations and photon blockade. If successful, the results will be a real breakthrough for quantum polaritonics and its perspective for real-world applications, such as networked non-linear cavities for quantum simulation with light.
Informal enquiries should be sent to Dr Hamid Ohadi (ho35@st-andrews.ac.uk).
[1] G. Munoz-Matutano et al, Nature Materials 18, 213–218 (2019).
[2] A. Delteil et al, Nature Materials 18, 219-222 (2019).
[3] Kazimierczuk et al, Nature 514, 343 (2014).
Semiconductor physics
Quantum optics and information
Strong matter-light coupling with novel materials
Polaritons are quasiparticles resulting from strong coupling between matter and light. Strong coupling occurs for photons confined in a microcavity, so that rather than photon emission being an irreversible loss process, photons that are emitted into the cavity can subsequently coherently excite the material again. This leads to new normal modes, polaritons. [1]
Historically, much of the work on these quasiparticles made use of strong coupling to electronic excitations in inorganic semiconductors, such as GaAs or CdTe. However, recently there has been a lot of interest in polaritons formed from a wide variety of materials, including organic molecules (ranging from small molecules to organic polymer chains), as well as very recent developments for materials such as transition metal dichalcogenides, and hybrid organic-inorganic perovskits. These molecular systems have very strong matter-light coupling, and so the physics can be seen at room temperature. [1,2]
One significant area of research concerns polariton condensation and lasing. Polaritons are bosons, and so Bose-Einstein condensation can be (and has been) seen. Because polaritons are part photon, they have a very low effective mass, leading to a very high transition temperature, indeed with organic materials, this can occur up to room temperature.
Another area of increasing experimental interest is in using strong coupling to change material properties. In the context of organic molecules, this has included the idea of changing chemical reaction rates by strong coupling.
This PhD position will be to explore theoretically models that capture the specific physics of a given material system, and ask how the physics of these materials affects, and is affected by, strong coupling to light. We will look both at the physics of Bose-Condensation, as well as modelling other possible applications of strong matter-light coupling to change material properties. We will make use of a variety of analytical and numerical techniques. For examples of our recent work see Refs. [3-5]
[1] "The new era of polariton condensates." D. W. Snoke and J. Keeling Phys. Today 70 54 (2017)
[2] "The road towards polaritonic devices." D. Sanvitto and S. Kena-Cohen. Nat. Mater. 15 1061 (2016)
[3] "Organic polariton lasing and the weak- to strong-coupling crossover" A. Strashko, P. Kirton, J. Keeling arXiv:1808.07683
[4] "Orientational alignment in cavity quantum electrodynamics." J. Keeling and P. G. Kirton. Phys. Rev. A 97 053836 (2018)
[5] "Exact States and Spectra of Vibrationally Dressed Polaritons." M. A. Zeb, P. G. Kirton, and J. Keeling. ACS Photonics 5 249 (2018)
Subdiffusive dynamics in the approach to many-body localisation
The phenomenon of many-body localisation � the failure of ergodicity in certain disordered, interacting many-body quantum systems � has become a major topic of research over the past few years [1]. Recently attention has also become focussed on the approach to this transition from the ergodic side. In particular, it has been shown that spin and energy transport become subdiffusive before the actual many-body-localisation transition is reached [2,3].
Recent work in my research group has concentrated on how universal such subdiffusive phenomena are [4]. In particular, we have begun investigating the connection between the hydrodynamics of the weakly disordered model and the nature of the subdiffusive transport that occurs in the approach to full localisation. The aim of this project is twofold: first, to extend those numerical studies to a larger class of one-dimensional models, and second, to draw on existing literature on the nonlinear Schr�dinger equation [5] to explore the development of an analytical theory of this subdiffusive regime.
[2] M. �nidaric, A. Scardicchio, and V.K. Varma, Phys. Rev. Lett. 117, 040601 (2016).
3] V.K. Varma, A. Lerose, F. Pietracaprina, J. Goold, and A. Scardicchio, J. Stat. Mech. (2017) 053101.
[4] M. Schulz, S.R. Taylor, A. Scardicchio, and C.A. Hooley, in preparation.
[5] A. Iomin, Phys. Rev. E 81, 017601 (2010).
Theory of Quantum Light Sources: how can we make coherent single photons in solid state systems?
The generation of indistinguishable single photons on demand is a key requirement for many kinds of future quantum technologies, such as secure communication and optical quantum computing [1]. Being able to make coherent quantum light sources in solid state systems would enable us to create on-chip photonic circuits that would enable this technology. It is therefore of the utmost importance to understand what effect a solid state environment has on the fidelity of emitted photons.
In this project, you will exploit and developing a groundbreaking new technique our group has created for simulating open quantum systems [2]. Based on a combination of Feynman's path integrals [3,4] and matrix product states [5], it has already enabled calculations impossible by more traditional means. You will study how the technique might be used to calculate the photon correlation functions that characterise a single photon source, in the presence of a strongly-coupled environment of vibrational modes of the crystal. You will go on to study how a photonic cavity might be used to improve the performance of such a device.
[1] I. Aharonovich. D. Englund and Milos Toth, Nature Photonics 10 631 (2016)
[3] R. P. Feynman, and F. L. Vernon, Jr., Ann. Phys. 24 118 (1963)
[4] N. Makri and D. E. Makarov. The Journal of Chemical Physics J. Chem. Phys. 102 4600 (1995)
[5] R. Orús, Annals of Physics 349 117 (2014)
Topological physics beneath magnetic structures and interfaces on superconductors
It has been known for a long time that magnetic impurities induce bound states in superconductors [1] but only in recent years it was realised that lining up such states [2] can lead to a twist in the resulting wave function that is known as a changed topological index. The study of such topological states has by now become a highly active field of research. A strong promotor is the rather recent insight that any quantum technology will have to rely on some form of topological states. In this PhD project we will investigate how topological properties appear at interfaces or magnetic structures embedded on superconductors, in a set-up where a strict dimensional decoupling as considered by most approaches is not possible. This will build on our recent work [3]. A particular emphasis will be given to interactions between the states generated by the interaction between the magnetic scatterers and the superconductor, and to particular instabilities that can lead to novel quantum phases.
[1] L. Yu, Acta Phys. Sin. 21, 75 (1965); H. Shiba, Prog. Theor. Phys. 40, 435 (1968); A. I. Rusinov, JETP Lett. 9, 85 (1969).
[2] F. Pientka, L. I. Glazman, and F. von Oppen, Phys. Rev. B 88, 155420 (2013); S. Nadj-Perge, I. K. Drozdov, J. Li, H. Chen, S. Jeon, J. Seo, A. H. MacDonald, B. A. Bernevig, and A. Yazdani, Science 346, 6209 (2014).
[3] C. J. F. Carroll and B. Braunecker, arXiv:1709.06093.
Topological Superconductivity
The concepts of symmetry and symmetry breaking cut across all sub-fields of physics. Whether crystal symmetry in solids, gauge symmetry in superconductors or time reversal symmetry in ferromagnets, we have become used to defining phases of matter in terms of order parameters associated with symmetry breaking. However, not all collective quantum states can be fully characterised in terms of their symmetries. In some systems phases are classified in terms of their topological characteristics. Although this has been known for several decades, it was thought to apply in highly restricted circumstances. Exciting and rapid developments over the past five years have shown that these topologically characterised phases are likely to be much more widespread than first thought, and that, in the long term, it may be possible to exploit their properties in adventurous new technologies. Although progress has been rapid, fascinating theoretical questions remain, not least the interplay between symmetry and topology. The field is also ripe for experimental study. Superconductors are among the most fascinating candidates for topological systems. A host of intriguing theoretical proposals exist, but the extent to which they are observable in practice has yet to be determined. This project is concerned with investigating candidate topological superconductors, using a combination of the world-leading experimental facilities in St Andrews, Dresden and Cornell. The project is ambitious, and would be best suited to a candidate with both experimental and theoretical aptitude.
Ultrafast control of correlated states in 2D materials
In recent years, it has become possible to fabricate materials down to just a single atom in thickness. Compared to their bulk counterparts, this nanostructuring approach can drive a host of major changes in their material properties, from electronic transport and optical activity to the way in which electrons in these systems interact with each other and the underlying crystal lattice in which they reside. A way to further control these interactions is via ultrafast (fs) laser excitation. Importantly, such excitation can now be combined with a precise probe of how the electron motion in solids is modified, via time- and angle-resolved photoemission spectroscopy (TR-ARPES). In this project, you will fabricate crystals in the two-dimensional limit using ultra-high vacuum-based growth techniques, and study the resulting electronic properties of the materials using both static and TR-ARPES techniques. A particular initial focus will be in the optical control of correlated and magnetic orders in these systems. This PhD project forms part of an ambitious research programme to be undertaken jointly between the Electronic Structure of Quantum Materials group at the University of St Andrews, Scotland (www.quantummatter.co.uk/king), and the Artemis program at the U.K Central Laser Facility, Rutherford Appleton Laboratory, in Oxfordshire (https://www.clf.stfc.ac.uk/Pages/Artemis.aspx). Your project will exploit a unique UK capability for integrated materials synthesis and electronic structure study in St Andrews (www.quantummatter.co.uk/research), and the recently-upgraded state-of-the-art capabilities for TR-ARPES at the Rutherford Appleton Lab (https://www.clf.stfc.ac.uk/Pages/100-kHz-IR-upgrade.aspx). You will be based in St Andrews for approximately half of the project, and in Oxfordshire for the other half, and will additionally attend synchrotron beamtimes at leading international facilities; a willingness to travel is thus an essential pre-requisite! Candidates should have a degree in physics or a related discipline. Laboratory experience with ultra-high vacuum techniques, synchrotron or laser science, or crystal growth is helpful but not required. For more information, contact charlotte.sanders@stfc.ac.uk or philip.king@st-andrews.ac.uk.
Ultrafast Photophysics of Organic Semiconductors
This project will explore the physics of remarkable plastic-like semiconductors, such as light-emitting polymers. These materials are model one-dimensional systems and this strongly influences their physics � for example it means that excitons are strongly bound and that there is a substantial distortion of the material when it is excited. The purpose of this project is to study the nature of the excited states in these materials and how they evolve when the sample is excited by light. The initial rearrangement of the molecules occurs on a timescale of 100 femtoseconds. Remarkably we can make measurements on this timescale using advanced femtosecond lasers. We wish to explore how the excited states form and then decay, and how these processes relate to the structure of the material. The results will help understand light emission and amplification, and complementary theoretical work is underway at Heriot-Watt University by Prof. Ian Galbraith.
Optimisation of interferometry-based volume holography for industrial applications
Di Falco, Prof Andrea - adf10@st-andrews.ac.uk
Joint project between School of Physics and Astronomy and ceres Holographic Ltd.
Volume holograms based on photopolymers are one of the most promising platforms to develop commercial applications of holographic optical elements at industrial level. Ceres Holographics' unique approach uses a bespoke interferometric process to create volume phase holograms in a proprietary photopolymer. The process is high yield and reliable and produces state-of-the-art holograms. A key factor to enhance further the quality and potentials of the manufacturing technique is to fully address the optical response of the photopolymer and minimise the occurrence of unwanted artefacts.
The aim of the project is to develop a detailed model of the photopolymer to unveil the relevant polymerisation and diffusion processes and to understand the optimum timing/exposure requirements. The investigation will be complemented by an extensive experimental activity, exploiting the facilities available in the School of Physics and Astronomy of the University of St Andrews and at Ceres Holographic.
The project funds in full a four years long PhD studentship, including fees and a stipend for eligible students. Successful applicants will be part of a small yearly cohort that will meet for networking, technical and MBA courses as well as professional skills workshops.
Degree in physical science (1st or 2:1 honours degree in physics or a related subject)
Background in Applied Optics
An interest in experimental physics
Knowledge of photochemistry
Programming skills for the automation of experiment and data analysis
Ceres Holographic and the School of Physics and Astronomy are located in the North Haugh scientific hub in St Andrews, at walking distance from each other. Academically, the student will be co-supervised by the Organic Semiconductor group and the Synthetic Optics group, who manage the cleanroom facilities in the School and have access to a large suite of characterisation laboratories. The student will have daily access to, and is encouraged to make maximum use of, the holographic fabrication and characterisation facilities at Ceres Holographics.
Polymer optoelectronics
Synthetic Optics
organic semiconductor polariton light emitters
Plastic Lasers
Conjugated polymers are a very special class of plastics that are both semiconducting and efficient light-emitters. They have been widely applied as flat and flexible light emitting displays, as well as visible lasers, optical amplifiers, solar cells and electronic circuits. As novel laser media, polymers are particularly attractive because they can be easily and inexpensively formed into flexible shapes and structures that are inaccessible to crystalline materials.
This project builds on our internationally recognised research programme in polymer lasers. We have demonstrated plastic lasers driven by a light-emitting diode and are currently developing lasers and optical amplifiers integrated with nitride LEDs and CMOS control electronics. Novel photonic nanostructures are used to control
laser emission, develop new modes of operation and applications in sensing and datacomms.
Smart lighting technology for growing algae
"Dial a wavelength" for exploiting the algal cell factory
This multi disciplinary project will be undertaken in collaboration with Prof Christine Edwards at Robert Gordon University, and Xanthella ltd in Oban. The project will include a substantial industrial placement at Xanthella to integrate and test the new lighting technology in Xanthella's photobioreactors.
Microalgae are of value in a wide array of applications including pharmaceuticals and food supplements. Most algae use light energy and CO2 for growth, providing valuable by-products whilst sequestering waste CO2. They are of increasing interest as components of the Circular Economy as sustainable solutions for food, energy and water security. Photobioreactors can be used to grow algae, making use of surplus electricity from renewable power generation, however, new smart-lighting systems are needed that can optimise production.
In this project a novel wavelength-tunable lighting system will be developed to provide broad spectrum illumination to the hotobioreactor, and/or can switch to target production of individual pigments including chlorophylls, carotenoids, phycobiliproteins. LEDs will be combined with a custom-built optical system to deliver light throughout the growth reactor. The impact of illumination wavelength will be assessed initially in laboratory-scale growth tests before subsequent scale-up and integration in industrial photobioreactors.
The main activities of the project will be designing and building the lighting system and algal growth tests. Training on algal culture and compound analysis will be undertaken at RGU. Once laboratory-scale tests have identified suitable growth methodologies, the lighting system will be adapted for integration with Xanthella's commercial 100 L and 1000 L photobioreactors.
Advanced Imaging for the Biomedical Sciences (with Dr F Gunn-Moore, School of Biology)
Cizmar, Dr Tomas - tc51@st-andrews.ac.uk
Dholakia, Prof Kishan - kd1@st-andrews.ac.uk
the aim of this project is to explore new routes for imaging both in vitro and in vivo using concepts of light transmission through disorder. In turn this will allow us to shape light at will for example at the end of an optical fibre and use this perhaps in an endoscopic scenarios. Other forms of microscopy to consider will involve using a light sheet for imaging larger biological systems (eg embryos). The study will involve advanced photonics, numerical studies and practical work. The research will also investigate strategies to image beyond the diffraction limit. Samples under investigation will include tissue and, at later stages of the work, potentially neuronal cells/tissue to target advanced understanding of neurological disease using these methods.
Biophotonics Collaboration
Advanced microscopy of nanolaser particles
Schubert, Dr Marcel - ms293@st-andrews.ac.uk
Nano- and microlasers have recently gained attention as novel light sources for biomedical applications, including single cell barcoding, refractive index sensing and tissue-integrated pressure sensors [1-3]. Their unique properties renders these devices ideally suited for experiments inside living specimens where many physical process related to development and disease are poorly understood.
Over the past decade, light sheet microscopy has revolutionized our understanding of the development of complex biological organisms [4]. While representing one of the most powerful and innovative microscopy techniques, light sheet microscopes are also typically build from scratch which allows to integrate a vast range of imaging modalities.
In this project, advanced 3D imaging will be combined with the broad capabilities of bio-integrated nanolaser. The goal is to correlate the spectroscopic information of the nanolasers with structural properties of the biological sample, by building a custom-made light sheet microscope. The new instrument will be used to investigate important biological processes like e.g. single cell tracking of invasive circulating tumour cells, cardiac regeneration or pressure sensing during gastrulation. Other aspects of the project are related to applying techniques to reduce effects of scattering by using advanced beam shaping techniques. Good knowledge of optics and microscopy, as well as basic programming skills are preferred but the student will be given the opportunity to learn relevant techniques during the project.
For further information please contact Marcel Schubert [ms293@st-andrews.ac.uk] prior to application.
[1] M. Schubert, A. Steude, P. Liehm, N. M. Kronenberg, M. Karl, E. C. Campbell, S. J. Powis, M. C. Gather, Lasing within Live Cells Containing Intracellular Optical Microresonators for Barcode-Type Cell Tagging and Tracking, Nano Lett. 2015, 15, 5647.
[2] M. Schubert, K. Volckaert, M. Karl, A. Morton, P. Liehm, G. B. Miles, S. J. Powis, M. C. Gather, Lasing in Live Mitotic and Non-Phagocytic Cells by Efficient Delivery of Microresonators, Sci. Rep. 2017, 7, 40877.
[3] A. H. Fikouras, M. Schubert, M. Karl, J. D. Kumar, S. J. Powis, A. di Falco, M. C. Gather, Non-obstructive intracellular nanolasers, arXiv:1806.03366, 2018.
[4] T.-L. Liu et al., Observing the cell in its native state: Imaging subcellular dynamics in multicellular organisms, Science 2018, 360, eaaq1392.
Aligning molecules to improve efficiency in next generation organic LEDs
Gather, Prof Malte - mcg6@st-andrews.ac.uk
Organic light-emitting diodes (OLEDs) are novel type of LEDs in which electroluminescence is generated by plastic-like organic molecules. OLEDs are at the heart of modern smart phone displays and are likely to become the dominant technology for computer screens and large area TVs in the future. In addition, OLEDs are considered for general illumination, an area where efficiency is of key importance. While OLEDs can operate with close to 100% internal electron-to-photon conversion efficiency, typically less than 20-25% of the generated light is extracted into the surrounding air; the rest is trapped in waveguided modes and eventually lost to absorption.
Various strategies have been proposed to improve light extraction from OLEDs. Very recently controlling the average orientation of the electroluminescent molecules inside an OLED has been identified as a promising avenue. However, accurate measurement of molecular orientation is difficult and it remains unclear how molecular orientation can be controlled efficiently. Within this project, these challenges will be approached by making use of different spectroscopic and computational methods. Provided certain formal criteria are met, the student can benefit from placement with a major commercial developer of OLED materials and technology.
A Graf, P Liehm, C Murawski, S Hofmann, K Leo, M C Gather, "Correlating the transition dipole moment orientation of phosphorescent emitter molecules in OLEDs to basic material properties", Journal of Materials Chemistry C 2, 10298 - 10304 (2014).
C Murawski, P Liehm, K Leo, M C Gather, "Influence of cavity thickness and emitter orientation on the efficiency roll-off of phosphorescent organic light-emitting diodes", Advanced Functional Materials 24, 1117-1124 (2014)
P Liehm, C Murawski, M Furno, B L�ssem, K Leo, M C Gather, "Comparing the emissive dipole orientation of two similar phosphorescent green emitter molecules in highly efficient organic light-emitting diodes", Applied Physics Letters 101, 253304 (2012).
Soft matter photonics
Biophysical Aspects of Photodynamic Therapy
Brown, Prof Tom - ctab@st-andrews.ac.uk
Photodynamic Therapy (PDT) is a treatment for cancer that involves light-activation of a photosensitiser and causes cell death by release of singlet oxygen and free radicals. The Scottish PDT Centre was established in Ninewells Hospital, Dundee in 2000 thanks to a generous donation from the Barbara Stewart Charitable Trust. Since its introduction in Dundee, over 2,000 treatments have been carried out. The photosensiters used for PDT also have the property that they fluoresce and so they can be used for photodiagnosis (PD), which is performed at the Scottish PDT Centre to direct the surgeon towards tissue that is likely to be cancerous.
The purpose of the proposed PhD program is to gain a fuller understanding of the interaction between the incident light and the tumour. Optimal treatment regimes have not been established. We would like to be able to model both PDT and PD. To assist in this, we propose to develop theoretical radiation transfer models using Monte Carlo techniques in order to simulate the incident light and the fluorescent emission. This will be done for the range of tissue types where PDT is performed in Dundee. This includes skin (the most accessible), the oral cavity, the brain and bladder.
The work will also find application in a wide range of other areas in the drive towards minimally invasive and highly targeted therapies. In addition to the PDT described above, the techniques can be applied to so-called �caged compounds� that are a range of biologically active compounds that are activated with light. In order to apply such compounds within a therapeutic environment, understanding the light tissue interactions is of key importance.
Light distribution measurements will be made around a range of light delivery devices, including cylindrical diffusers and miniature balloons filled with light-scattering media. Further measurements will be carried out using optical fibres embedded in tissue samples and using ultrashort pulses to probe two-photon activation at depth within the body. Fluorescent emission spectra will also be measured using a specially constructed optical biopsy system.
This project provides many opportunities for the student to study PDT and other light activated therapies from theoretical, experimental, and clinical perspectives.
There will be joint supervision from Dr Harry Moseley, who is Technical & Scientific Director of the Scottish PDT Centre and Honorary Reader at the University of Dundee, and Drs Tom Brown and Kenny Wood, who are Lecturers in the Department of Physics and Astronomy at the University of St Andrews. Dr Wood will supervise the theoretical aspects of the PhD (Monte Carlo radiation transfer), Dr Brown the experimental light tissue studies and Dr Moseley will supervise the clinical applications at Ninewells Hospital.
Giant Rydberg polaritons
Exploiting the laws of quantum mechanics for the benefit of humanity in the so-called "second quantum revolution" is one of the greatest challenges of the 21st century. For this we need to efficiently produce particles, control their states, detect them and make them interact strongly at the single-particle level. Photons, the quantum particles of light, are one of the most promising candidates. We can easily detect and control their states and we can efficiently produce them individually. However, making them interact strongly to build a large quantum network is a notoriously difficult task because photons do not interact at low energies. To make them interact indirectly, one can hybridise them with other massive particles that strongly interact and form quasiparticles called 'polaritons'.
In this project, we aim to hybridise photons with Rydberg excitons [1]. Rydberg excitons are highly excited (principal quantum number n~20) electron-hole pairs that can span macroscopic dimensions. Because of their macroscopic dimensions they strongly repel. The semiconductor device that we have chosen for hybridisation is a 2-dimensional semiconductor microcavity formed by two highly reflective mirrors encapsulating a cuprous oxide microcrystals and thin film. Photons confined in the microcavity strongly couple to Rydberg excitons in cuprous oxide to form Rydberg polaritons. This will allow us to explore quantum optics at the single-particle limit and form 2-dimensional networks of strongly correlated photons for future quantum simulators.
Hawking radiation in the laboratory
Koenig, Dr Frieder - fewk@st-andrews.ac.uk
Black holes can be understood in a simple picture: Imagine a river flowing towards a waterfall with ever increasing flow speed. Also imagine fishes in the river swimming upstream. At some position in the river the maximum speed of the fish will equal the flow speed and all fish beyond that "point of no return" will be flushed into the waterfall. Here the flow speed corresponds to the gravity of a black hole and the point of no return to the event horizon.
Arguably the most facinating aspects of astronomical black holes is the emission of Hawking radiation from the event horizon, an intriguing quantum effect combining gravity, thermodynamics and quantum mechanics.
Unfortunately, the astrophysical Hawking radiation is far too weak to ever being detected directly. Recently, however, we have invented a method to create moving artificial event horizons with short pulses in optical fibers. Moreover, the expected Hawking radiation is strong enough to be detectable with single photon coincindence counting.
The idea of the PhD programme is the calculation, detection, and characterization of this elusive Hawking radiation for the first time. The work has already gained momentum in our group and a setup is built using optical pulses of just a few cycles pulse length. In addition we will explore further quantum field theory effects in curved spacetime.
Experimental quantum optics
Linear and nonlinear properties of 3D optical Metamaterials.
Metamaterials (MMs) are man made materials with engineered optical properties. They are made assembling their artificial atoms at a scales much smaller than that of light, so as to appear homogenous. They are at the basis of very thought provoking proposals, including super imaging and cloaking applications.
In the group of Synthetic Optics we have developed a large portfolio of fabrication techniques for one- and two-dimensional MMs.
The aim of this project is to develop the fabrication protocol and applications of three-dimensional MMs obtained with a bottom up approach. The student will combine the extraordinary physical and optical properties of silica based aerogels with the flexibility of the design of nanoplasmonics to realise effective materials with bespoke optical behaviour. The aerogel is an ultra light material with refractive index close to unity and thermally more insulating than air. Combining these features with the field enhancement offered by infiltrated metallic nano particles is specially suited to address nonlinear effects at ultra-low powers.
This challenging but rewarding project requires a thorough understanding of the physics involved and the experimental rigour to fabricate and test the MMs, but offers the student the chance to learn a broad range of design, fabrication and experimental techniques.
Living Lasers: Lasing from biological cells
Optical phenomena in biological structures have fascinated mankind for centuries and biological materials with optical functionality are currently a major topic of research. In the future, photonic devices may indeed be based on natural or genetically engineered optical function.
Recently, we developed a biological laser � a device based on a single living cell genetically programmed to produce the fluorescent protein GFP. The laser is biocompatible and biodegradable, and thus offers unique physical and biological properties not shared by any existing device.
However, so far our biolasers require an artificial resonator and an external pump source. This project is aimed at gaining a better understanding of lasing and stimulated emission in biological materials and at developing new avenues to biolasers. For example, this can include the study of bio-assembled resonators based on naturally occurring structures, photophysical investigations aimed explaining why fluorescent proteins are such efficient laser materials, or the development of biocompatible nanolasers.
The project is inter-disciplinary, involving photonics, laser physics, genetic engineering, proteomics, and material science and adequate training in these fields will be provided within the school and through external collaborators.
M C Gather, S H Yun, "Single-cell biological lasers", Nature Photonics 5, 406-410 (2011)
M T Hill, M C Gather, "Advances in Small Lasers", Nature Photonics 8, 908-918 (2014) (Review paper)
M C Gather, S H Yun, "Bio-optimized energy transfer in densely packed fluorescent protein enables near-maximal luminescence and solid-state lasers", Nature Communications 5, 5722 (2014)
C P Dietrich, S H�fling, M C Gather, "Multi-state lasing in self-assembled ring-shaped eGFP microcavities", Applied Physics Letters 105, 233702 (2014)
Millimetre wave radar signatures of drones
The detection of small unmanned aerial vehicles (UAVs), or drones, is a growing requirement both for the management of intentional drone activity and for the detection of unwanted drones which might cause a risk to security, safety or privacy. Radar is one of the most promising sensors with which drones can be detected and classified by using distinct radar signatures such as radar cross section (RCS) and micro-Doppler (produced by the rotation of the propeller blades). Research in the Millimetre Wave Group has shown that millimetre wave radar may offer some advantages in drone detection, tracking and classification in terms high Doppler sensitivity and compact system size. This PhD project aims to deepen the understanding of the millimetre wave radar signatures of drones and develop techniques which could be applied in a drone detection system. The scope of research topics includes:-
1.	Develop statistical fluctuation models to analyse RCS characteristics of drones at millimetre-wave frequencies using data available at St Andrews.
2.	Characterise RCS values of drones in terms of fuselage and propeller material, size, shape and aspect angles.
3.	Study polarisation dependencies of the RCS values of the drones at millimetre-wave frequencies by using the available data and acquiring more data by using radars available at St Andrews.
4.	Develop EM scattering models of commercial drones to study and characterise the micro-Doppler signatures produced by the propellers. Understanding of the features will be further strengthened by lab-based controlled environment experimental data collection and analysis.
5.	Wavelet analysis of the micro-Doppler signatures of drones. Develop wavelet signature based drone classification algorithm for real-time application.
6.	Inverse Synthetic Aperture Radar (ISAR) imaging of drones using high resolution range profiles (HRRP) data. Study the feasibility of distinguishing attached payloads and different models of drones using ISAR data.
7.	Develop techniques for Neural Network based drone classification algorithm for real-time application. Extensive data is already available at St Andrews to create a training database. The candidate will also design and set up experimental trials to make the database larger and more diverse in terms of number of drones and surrounding environment.
The candidate should have a degree in Physics or Electronic Engineering, ideally with some knowledge of radar, signal processing or microwave technology. Familiarity with MATLAB and C programming would be an advantage.
The Millimetre Wave Group (https://www.st-andrews.ac.uk/~mmwave/) is extremely well equipped with test equipment, measurement facilities including an outdoor test range with dedicated lab, and a large array of components and subsystems enabling rapid development. We have built 13 radar systems at frequencies of 24, 77, 38, 94, 220 and 340 GHz, many of which would be available for data collection in this project.
If you are interested in this PhD project please contact the supervisor Dr Duncan A. Robertson (dar@st-and.ac.uk) to discuss it further.
Robertson, Dr Duncan - dar@st-andrews.ac.uk
Millimetre-wave physics and THz technology
MM-wave Radar, Components and Techniques
Smith, Prof Graham - gms@st-andrews.ac.uk
MM-waves represent the area of the electromagnetic spectrum that sits between microwaves and Terahertz frequencies. It is the part of the spectrum where electronics meets optics and a wide variety of physical techniques are used to design components and systems. MM-waves are used in high resolution radar, fusion diagnostics, earth resource studies, magnetic resonance and security systems.
The mm-wave group at St Andrews is one of the largest and most well established groups in this field in the UK, and has a strong track record in designing components, sub-systems and full system. Much recent work ahas concentrated on developing radar imaging systems for earth resource studies (imaging volcanos, monitoring rainfall) and for various security related systems.
There is also a very strong program in mm-wave magnetic resonance.
A variety of PhD topics are always available and any interested student should get in touch with Dr Graham Smith in the first instance.
New photonics tools unravel the mysteries and mechanics of biological cells
Biologists have compelling evidence that in addition to biochemical signals, mechanical forces have a major impact on a wide range of processes in cell biology, with examples ranging from cell migration and cell growth to the spreading of cancer and the differentiation of stem cells. However, there is at present a shortage of suitable tools to measure the force exerted by a cell which often is well below 1nN (i.e., < 10-6�N (!)).
By developing a novel optical micro-cavity-based sensor technology, the Gather Lab seeks to overcome current limitations in measuring cellular forces and � for instance � investigate the mechanics involved in the formation and the growth and repair of nerve cells.
The basic working principle of our sensors is to detect shifts in the resonance frequency of a micro-cavity due to mechanical forces applied by cells cultured on the sensor. These shifts can be detected with high spatial and temporal resolution and the forces at play are then computed from this by a finite element method.
A PhD in the field of cellular mechanics provides you with a broad, interdisciplinary skill set: You will learn and apply a range of micro- and nano-fabrication methods and work in a state-of-the-art cleanroom. You will use different types of optical spectroscopy and work with atomic force microcopy. You will receive hands-on training in cell culturing techniques and perform studies of e.g. stem cell differentiation.
The project is part of an international collaboration with leading scientists at Harvard Medical School and University of Cambridge which is funded by the Human Frontier Science Program, the leading funding institution for interdisciplinary and international collaborative research into complex biological systems.
Non-reciprocal optics
Schulz, Dr Sebastian - sas35@st-andrews.ac.uk
In contrast to traditional, reciprocal optical systems, non-reciprocal systems allow the realization of interesting physical effects, for example optical isolation or the breaking of seemingly fundamental physical limits, such as the link between a system�s delay and its bandwidth [1]. Typically, non-reciprocal optical elements are realized using magneto-optic materials, for example in a Faraday Rotator. However, these materials are not suitable for integration in nanophotonic devices and thus new methods of achieving non-reciprocity need to be explored, for example nonlinear optical effects or time-variant modulations [2-4].
This project addresses the realization of on-chip non-reciprocal optical elements, new applications enabled by these elements and the exciting new physics achieved by combining non-reciprocal elements with components such as absorbers, emitters or resonators [1].
You are expected to have an interest in studying fundamental concepts in physics as well as mastering hands on nanofabrication and laboratory techniques. The project includes collaborations with groups across Europe and North America, offering you opportunities to visit the laboratories of collaborators and to build your own professional network.
The project will be supervised by Dr. Sebastian Schulz, who will join the department in March 2018. For more details on this topic and for any question regarding the project, please contact Dr. Sebastian Schulz (Sebastian.Schulz@cit.ie).
[1] H. Tsakmakidis, L. Shen, S. A. Schulz, X. Zheng, J. Upham, X. Deng, H. Altug, A. F. Vakakis and R. W. Boyd �Breaking Lorentz reciprocity to overcome the time-bandwidth limit in physics and engineering� Science 356, pp1260-1264 (2017). http://science.sciencemag.org/content/356/6344/1260
[2] E. A. Kittlaus, N. T. Otterstrom and P. Rakich �On-chip inter-modal Brillouin Scattering� Nature Communications 8, p.15819 (2017). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5504300/
[3] L. Feng, M. Ayache, J. Huang, Y.-L. Xu, M.-H. Lu, Y.-F. Chen, Y. Fainman and A. Scherer �Nonreciprocal Light Propagation in Silicon Photonic Circuit� Science 333, p. 729 (2011). http://science.sciencemag.org/content/333/6043/729
[4] D. L. Sounas and A. Alu �Non-reciprocal photonics based on time modulation� Nature Photonics 11, p 774 (2017). https://www.nature.com/articles/s41566-017-0051-x
Nonlinear Optical Micromanipulation
New uses of trapped colloid as nonlinear media and uses for observations of soliton-like waves and new forms of in-situ imaging as well as nonlinear processes (eg 4 wave mixing). This is a very exciting project based on novel ordering of colloidal particles in the presence of light fields as well as the use of these colloids as new media for nonlinear effects.
Optical Manipulation Group
OLED micro-displays as biophotonic platform
Organic Light Emitting Diodes (OLEDs) are novel optoelectronic devices with potential applications ranging from displays (e. g. in smart phones or for flexible screens) to general illumination. In contrast to conventional LEDs, OLEDs are based on plastic-like organic materials. Thus, they can be mechanically flexible and are believed to offer improved biocompatibility.
In this project, micro-displays based on >200,000 individual OLEDs, each smaller than a single biological cell, are used as a platform for advanced studies in cell biology. Potential applications include lens-free, low-cost, continuous microscopy of cells and structured illumination for optogenetic studies. Optogenetics is a technique which allows controlling the biological activity of genetically modified cells by exposure to light. Over the past decade, the technique has greatly improved the understanding of various fundamental processes in biology, in particular in neuroscience. OLED micro-displays may enable optogenetic experiments, like stimulating growth or movement of neurons, with improved temporal and spatial control, higher degree of parallelization and over longer times than currently possible.
This project is highly interdisciplinary involving photonics and materials science but also cell biology and genetics. Training will be provided in all these aspects from within my group and through collaboration with the School of Biology and external collaborators at University of Cambridge and Harvard Medical School.
L Fenno, O Yizhar, K Deisseroth (2011). The development and application of optogenetics. Annual Review of Neuroscience 34 (1), 389�412. DOI: 10.1146/annurev-neuro-061010-113817.
B Geffroy, P Le Roy, C Prat (2006). Organic light-emitting diode (OLED) technology: materials, devices and display technologies. Polym. Int. 55 (6), 572�582. DOI: 10.1002/pi.1974.
G Miller (2006). Shining new light on neural circuits. Science 314 (5806), 1674�1676. DOI: 10.1126/science.314.5806.1674.
optical antennas for visible light communications (Li-Fi)
Visible light communications is an emerging field that aims to deliver high-bandwidth wireless data through solid-state (LED) lighting. This project will be part of a multi-disciplinary research collaboration between the Universities of St Andrews, Strathclyde, Edinburgh, Oxford and Cambridge which will develop the next generation VLC technology.
The aim of this project will be to develop nanophotonic hybrid light sources and detectors based on luminescent polymer films. The student will design novel optical antennas, and fabricate these using thin film depostion and nanoimprint lithography. Working with the partner universities, these components will be combined with gallium nitride LEDs and CMOS detectors to develop next generation tranceiver technologies for visible light communications.
Optical Imaging of Biological Specimens
ptical imaging can provide detailed information about a range of biological specimens from whole animals to small tissue samples. A drawback however is that such imaging often only provides data from structures at or near the surface. By contrast Optical Coherence Tomography (OCT), a low coherence interference imaging technique, can provide detailed information on tissue structure at depths of a few mm with resolution of around 10 um in living animals.
In this project we will apply OCT to a range of biological specimens to provide information which has proved to be unobtainable using other techniques. In particular the project will use OCT to provide information on tissue regeneration in amphioxus (fish-like marine chordates with close affinity to vertebrates) which are used as a model for testing concepts in nerve cord growth and repair. We will also apply OCT to Antarctic Krill (Euphasia superba), perhaps the key species in the Antarctic food web. The information these studies provide will be used to develop advanced models for acoustic imaging Krill and may also support studies on the effects of global climate change on this key species. We may also apply the system to recently launched studies of surface vasculature in Southern Elephant Seals to support ongoing studies into the diving physiology of this species.
The projects described are interdisciplinary and will require an open mind and a willingness to work with partners within Biology and Marine Science in the UK and at the Australian Antarctic Division. Australia. In order to fully develop our systems and to enable in vivo testing some travel and extended stays may be required to partner institutions.
The main supervisor for the project will be Professor Tom Brown in the School of Physics, with co-supervision by Dr Ildiko Somorjai within the School of Biology.
Prospective students should have a good background in Physics with an interest in applying their work in other fields. We are also interested in applications from students in Biology who have a strong background in imaging techniques.
Examples of the application of OCT to Krill can be found at:
M.J. Cox, S. Kawaguchi, R. King, K.Dholakia and C.T.A. Brown, �Internal physiology of live krill revealed using new aquaria techniques and mixed optical microscopy and optical coherence tomography (OCT) imaging techniques�, Marine and Freshwater Behaviour and Physiology, 48, p. 455 (2015)
N. Bellini, M.J. Cox, D.J. Harper, S.R. Stott, P.C. Ashok, K. Dholakia, S. Kawaguchi, R. King, T. Horton and C.T.A. Brown, �The Application of Optical Coherence Tomography to Image Subsurface Tissue Structure of Antarctic Krill Euphausia superba�, PLOS ONE, 9, Art. No. e110367 (2014
Optical manipulation: air/vacuum trapping for cavity optomechanics
Optical trapping leads to the confinement of microscopic and nanoscopic objects using light. In the domain of optomechanics we would like to cool small "trapped" mechanical oscillators down to the quantum regime. This project aims to experimentally explore new ways to levitate and trap microparticles in air and vacuum. The ultimate aim is to slow down or 'cool' spheres to the ground state of motion. The topic is currently one of the most exciting and rapidly growing areas of physics and will involve both theory and experiment.
Optomechanical Metasurfaces for Biophotonics Applications
The Synthetic Optics group (www.st-andrews.ac.uk/physics/synthopt) in the School of Physics and Astronomy at the University of St Andrews has a large portfolio of research projects aimed at designing and exploiting light matter interactions at the nanoscale. The range of applications targeted is equally wide and includes the development of advanced materials, nonlinear and complex photonic and biophotonics applications. All these strands converge in the newly funded project "AMPHIBIANS", which aims at developing a novel biophotonic platform based on the all optical manipulation of photonic metasurfaces in microfluidic environments. This experimental PhD project will focus on the design and fabrication of the photonic metasurfaces.
The current trend in biophotonics is to try and replicate the same ease and precision that our hands, eyes and ears offer at the macroscopic level, e.g. to hold, observe, squeeze and pull, rotate, cut and probe biological specimens in microfluidic environments. The bidding to get closer and closer to the object of interest has prompted the development of extremely advanced manipulation techniques at scales comparable to that of the wavelength of light. However, the fact that the optical beam can only access the microfluidic chip from the narrow aperture of a microscopic objective limits the versatility of the photonic functions that can be realized.
AMPHIBIANS aims to introduce a new biophotonic platform based on the all optical manipulation of flexible photonic metasurfaces. These artificial two-dimensional materials have virtually arbitrary photonic responses and have an intrinsic exceptional mechanical stability. This cross-disciplinary project, bridging photonics, material sciences and biology, will enable the adoption of the most modern and advanced photonic designs in microfluidic environments, with transformative benefits for microscopy and biophotonic applications at the interface of molecular and cell biology.
This experimental project is a unique opportunity for a motivated individual to work at the forefront of a cross-disciplinary and timely topic. The project is challenging but highly rewarding as it gives to the student the opportunity to learn different and highly valued skills, from the advanced design of nanophotonic devices, to the fabrication and characterisation of metasurfaces in the visible range and their applications to biological problems.
Organic light-emitting diodes
Visible light emission can be stimulated by applying a voltage to a thin layer of an organic semiconductor. The light emitted provides a window on the physics of the material, enabling us to learn about the nature of the excited states in the material. It is also useful for information display, lighting, and even for the treatment of skin cancer. We have developed a new class of light-emitting organic semiconductor, which could be used for high efficiency lighting, thereby reducing energy consumption.
Organic Solar Cells
The energy crisis is probably the most important problem facing the world today. Sunlight is the most abundant renewable energy source, but at present the cost of photovoltaics is too high for solar cells to be a serious alternative to fossil fuels. Organic semiconductors offer the prospect of low cost solar cells, but their efficiency needs improvement. We are working on new measurements to understand organic solar cell operation, and new materials to improve it.
Quantum interferometry
Interferometers are the most sensitive instruments for measuring length. This was demonstrated by the LIGO collaboration by the direct detection of gravitational waves, which was awarded the Nobel prize in 2017.
One might wonder what the limit of precision is in an optical interferometer. The answer is that the precision is limited by the combined effect of quantum uncertainty in the phase of light and quantum-radiation pressure on the mirrors of the interferometer. This is normally referred to as the standard quantum limit.
Manipulating cleverly the quantum state of light used in the interferometer, this limit can be overcome though. The typical idea is to inject a squeezed state of light into the interferometer to reduce the quantum noise in the single variable that is read out. However, this technique is susceptible to losses and noise in the squeezed state preparation and light detection.
Recently, an alternative way has been demonstrated, an SU(1,1) interferometer, in which the beam splitters of the interferometer are
exchanged with two-mode squeezers (parametric amplifiers) [3,4]. This interferometer is sensitive to losses only inside the interferometer arms, but does not require non-classical, quantum state injection or quantum-sensitive detection.
In this PhD program, the parametric process of four-wave mixing (FWM) in optical fibers is to be used to construct a robust fiber-integrated SU(1,1) interferometer with sub-shot noise sensitivity.
In the planned experiment, a strong pump light is propagated along a suitable photonic-crystal fiber. The FWM will lead to the spontaneous conversion of pairs of pump photons to two other light modes, the signal and idler beams, defined by their frequencies. If the process has very high gain and is not entirely spontaneous, but seeded by injecting a signal, high photon numbers can be achieved at the fiber output, maintaining the strong quantum correlations between signal and idler. The quantum state of light is referred to as 'bright squeezed vacuum' [1].
Thus in a second stage of the project, this light will be used in interferometry, in which the reverse FWM interaction creates nonlinear interference between the produced signal and idler beams. The increase in sensitivity compared to a linear classical interferometer scales as the square root of the photon number in the interferometer, beating the classical shot noise limits of interferometers.
The project involves pulsed as well as continuous lasers, fiber optics, spectrometry, and single photon counting.
The project will be carried out in collaboration and intellectual exchange with Prof. Chekhova at the Max Planck Institute of Light, Germany.
[1] I.N. Agafonov, M.V. Chekhova, and G. Leuchs, Two-Color Bright Squeezed Vacuum. Phys. Rev. A 82, 011801(R) (2010).
[2] Horoshko, D., Kolobov, M., Gumpert, F., Shand, I. R., Koenig, F. E. W., Chekhova, M., Journal of Modern Optics, 2019, "Nonlinear Mach-Zehnder interferometer with ultrabroadband squeezed light" https://www.tandfonline.com/eprint/8HRHTK8PJVKEGJ8ZWMTY/full?target=10.1080/09500340.2019.1674394
[3] B. Yurke, S. L. McCall, J. R. Klauder, "SU(2) and SU(1,1) interferometers", Phys, Rev. A 33, 4033, 1986.
[4] Mathieu Manceau, Gerd Leuchs, Farid Khalili, and Maria Chekhova, "Detection Loss Tolerant Supersensitive Phase Measurement with an SU(1,1) Interferometer", Phys. Rev. Lett. 119, 223604 2017.
Single photon optical eigenmodes
Mazilu, Dr Michael - mm17@st-andrews.ac.uk
Structured light is used in imaging, communication and optical micromanipulation to increase resolution, data capacity and optimise optical traps. At the single photon level, structured light offers the perfect system to study fundamental light-matter interaction such as the transfer of linear and angular momentum to microscopic objects. This theoretical study looks at the links between quantum technology and optical micromanipulation. More precisely, coherent electromagnetic radiation can take many forms in general. Indeed, any scattering and interaction of a light field with its environment will change the beam profile and the properties of the light field involved. These effects can be calculated numerically and sometimes analytically by solving the classical Maxwell�s equations. One class of solutions of Maxwell�s equations are the optical eigenmodes that constitute a natural representation of electromagnetic scattering events. These eigenmodes are orthogonal to each other and are useful to optimise beam properties such as linear and angular momentum transfer to microparticles. This is particularly interesting when designing structured illumination for optical micromanipulation, coherent control, single pixel imaging super resolution microscopy and spectroscopy. This project aims at expanding our initial research looking at the use of optical eigenmodes in the context of single photons and quantum optics. The project has a numerical and a theoretical component that together should enable the results to be applicable to experimentally relevant cases.
Single-molecule spectroscopy of organic semiconducting polymers
Penedo-Esteiro, Dr Carlos - jcp10@st-andrews.ac.uk
Organic semiconductors based on light-emitting conjugated polymers are attracting considerable interest in semiconductor physics and are emerging as exceptional �plastic-like� materials for optoelectronic applications including displays, lasers and solar cells. We have recently reported the first single-molecule studies regarding the conformation of individual polymer chains in organic solvents commonly used for device fabrication [1 ,2]. Now, in this project, we aim to combine this observation method based on single molecule fluorescence spectroscopy with magnetic tweezers to apply force to the polymer chain. By merging both techniques we will be able to stretch the polymer chain at will and understand in more detail how the conformation of the polymer chain impacts its light-emission properties. The results will help to develop new solution-processing methods that improve device performance. The project is a collaboration between the groups of Prof Ifor Samuel and Dr Carlos Penedo
[1] Dalgarno, Paul A., Christopher A. Traina, J. Carlos Penedo, Guillermo C. Bazan, and Ifor D. W. Samuel. 2013. �Solution-Based Single Molecule Imaging of Surface-Immobilized Conjugated Polymers.� Journal of the American Chemical Society 135 (19): 7187�93.
[2] Tenopala-Carmona, F., S. Fronk, Gui Bazan, Ifor DW Samuel, J. Carlos Penedo. (2018) Real-time observation of conformational switching in single conjugated polymer chains. Sci. Adv. In press
Slow and structured light in nanophotonics
Slow light waveguides have the potential to strongly enhance light matter interactions, leading to efficient non-linear optical processes, optical switches and optical modulators amongst other applications [1]. On a photonic chip slow light is typically realized through Photonic Crystal waveguides or coupled optical resonator waveguides [2], with the speed of light typically between 1/ 10 and 1/100 of the free space value. However, all these realizations suffer from optical scattering from fabrication defects [2-4], leading to optical losses and light localization, limiting the current device performance and rendering physical concepts such as the group velocity meaningless. Yet at the same time optical information can travel through completely opaque materials, implying that the current limit � not using photonic devices in the strong scattering regime - is self-imposed.
In this project you will investigate new slow light waveguide designs, leading to further reductions in the group velocity, while simultaneously reducing the optical losses and scattering. You will address fundamental questions about the behaviour of light and information in scattering media, for example: �At what velocity does information travel through a disordered system and how is this dependent on the disorder level in the system?�. You will investigate the effect of slow light on topics at the forefront of integrated photonics research, for example the use of complex polarization states in integrated optics and how this is affected by the disorder present in real world systems.
You will learn nanofabrication, optical simulation and characterisation techniques and gain a deep understanding of complex physical systems. You will interact with collaborators both in the UK and abroad, giving you the opportunity to visit their laboratories and build your own professional network.
[1] T. F. Krauss �Why do we need slow light� Nature Photonics 2, p 448-450 (2008). https://www.nature.com/articles/nphoton.2008.139
[2] S. A. Schulz, L. O�Faolain, D. M. Beggs, T. P. White, A. Melloni and T. F. Krauss �Dispersion engineered slow light in photonic crystals: a comparison� Journal of Optics 12, 104004 (2010). http://iopscience.iop.org/article/10.1088/2040-8978/12/10/104004/meta
[3] S. Mazoyer, J. P. Hugonin and P. Lalanne �Disorder-induced Multiple scattering in Photonic-Crystal Waveguides� Physical Review Letters 103, 063903 (2009). https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.103.063903
[4] L. O�Faolain, S. A. Schulz, D. M. Beggs, T. P. White, M. Spasenovic, L. Kuipers, F. Morichetti, A. Melloni, S. Mazoyer, J. P. Hugonin, P. Lalanne and T. F. Krauss �Loss engineered slow light waveguides� Optics Express 18, pp.27627-27638 (2010). https://doi.org/10.1364/OE.18.027627
Sub-THz Radar sensing of the Environment for future Autonomous Marine platforms (STREAM)
Funding for this PhD will be available from the School of Physics & Astronomy's strategic DTP allocation or other university scholarship.
This PhD will complement the 3.5 year STREAM project, a £1.5M EPSRC funded collaboration between the University of St Andrews and the University of Birmingham. STREAM aims to develop advanced sub-THz radar systems that will enable true autonomy for marine systems, by providing situational awareness in a dynamic sea environment and obscuring conditions
Research on autonomous ground vehicles, guided by various sensors (lidar, acoustic, radar), has existed for many decades and the technology is now relatively mature. In contrast, research in autonomous operation in the marine environment is less mature but evolving rapidly. The key enabler will be the role of advanced electronics to provide vessels with full intelligence to facilitate autonomous operation with sensing and processing capabilities superior to those of a human.
The requirements for sensing capabilities to provide situational awareness to small and medium vessels in the dynamic marine environment include (i) maintaining safety of the boat and humans and animals in the water which requires the robust all-weather day/night detection and classification of objects in the water and (ii) adaptive path planning which requires wave profiling of the local sea surface and the detection of hazardous large waves. We assert that the key sensor modality to satisfy these requirements is novel sub-THz radar operating in the 140-340 GHz frequency spectrum. Sub-THz radar offers the advantages of very high resolution sensing with very compact sensors and the ability to penetrate obscuring conditions. Such radars will be able to measure a range of parameters from the sea surface and objects within it including range, cross-range, bulk Doppler, micro-Doppler and radar cross section (RCS). This information can then be processed to detect, track and classify objects in the scene and provide information to decision making tools used in the control of autonomous vessels.
During this PhD the candidate will collaborate very closely with the wider research team of colleagues in the Sea Mammal Research Unit at St Andrews and in the Microwave Integrated Systems Laboratory (MISL) at the University of Birmingham, plus our broad range of industrial Project Partners who are supporting the project.
The research will focus strongly on the field collection of radar data at maritime locations around the UK during multiple field trips – currently there is an almost complete lack of data on sub-THz properties of the marine environment so a primary aim of the project is to collect extensive data sets. Based on these data sets, research tasks will include:
•	Modelling and analysis of sub-THz sea clutter
•	Modelling and analysis scattering from objects in the sea including sea mammals
•	Modelling and analysis of atmospheric propagation effects in the marine boundary layer
•	Development of signal processing algorithms for detection & tracking
•	Development of image analysis and classification methods
•	Investigation of adaptive waveform design suitable for cognitive radar operation
The Millimetre Wave Group (https://www.st-andrews.ac.uk/~mmwave/) is extremely well equipped with test equipment, measurement facilities including an outdoor test range with dedicated lab, and a large array of components and subsystems enabling rapid development. We have built 13 radar systems at frequencies of 24, 77, 38, 94, 220 and 340 GHz, several of which would be available for data collection in this project. The group also has EM simulation and modelling facilities including CST Microwave Studio.
The Development of Ultrafast Laser Systems
Ultrafast laser systems generate short pulses of light which may last on a few femtoseconds (fs.) These lasers are used in a wide range of applications from highly sensitive metrology to the 3D imaging of biological specimens.
In this project, we will continue our develops of ultrafast laser systems based on novel-glass gain media supplied by our partners within the UK. The student will be responsible for the design and operation of new laser systems. We will also use these systems to test advanced new components including saturable absorbers based on e.g. graphene and MoS2 and testing new approaches for dispersion compensation. As the project progresses we will also investigate the development of integrated ultrafast sources combining with other staff in the School of Physics and Astronomy and further afield. The lasers developed will be used in a range of new applications including the development of new techniques in dentistry where we will replace worn out enamel using laser sintered materials.
Students undertaking this project should have an interest in lasers and photonics systems. Experience of work within an advanced photonics laboratory would be advantageous (though not necessary) and students should be prepared to work closely with collaborators around the work to develop the laser systems.
Examples of previous work within the group can be seen at:
A. Choudhary, A.A. Lagatsky, Z.Y. Yang, K.J. Zhou, Q. Wang, R.A. Hogg, K. Pradeesh, E.U. Rafailov, W. Sibbett and C.T.A. Brown, �A diode-pumped 1.5 mu m waveguide laser mode-locked at 6.8 GHz by a quantum dot SESAM�, Laser Physics Letters, 10, Art. No. 105803 (2013)
N.K. Metzger, C.R. Su, T.J. Edwards and C.T.A. Brown, �Algorithm based comparison between the integral method and harmonic analysis of the timing jitter of diode-based and solid-state pulsed laser sources�, Optics Communications, 341, p.7 (2015)
A.D. Anastasiou, S. Strafford, O. Posada-Estefan, C.L. Thomson, S.A. Hussain, T.J. Edwards, M. Malinowski, N. Hondow, N.K. Metzger, C.T.A. Brown, M.N. Routledge, A.P. Brown, M.S. Duggal and A. Jha, �β-pyrophosphate; a potential biomaterial for dental applications�, In Press, Materials Science & Engineering C (2017)
A.A. Lagatsky, Z. Sun, T.S. Kulmala, R.S. Sundaram, S. Milana, F. Torrisi, O.L. Antipov, Y. Lee, J.H. Ahn, C.T.A. Brown, W. Sibbett and A.C. Ferrari, �2 �m solid-state laser mode-locked by single-layer graphene�, Applied Physics Letters, 102, Art. No. 013113 (2013)
Nonlinear Optics Group
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