substitution of Fe atoms for those with various ways such as F-doping of oxygen larger radius would increases lattice or simply by creating oxygen deficiency parameter a and b, while decreases [5]. This is however not always the case parameter c. Imagine having a network [11]. of closely packed oranges on one For those that superconducts after surface, with another layer of apples on the structural and magnetic transitions top, by replacing the oranges with are suppressed, there have been various watermelons, one should be able to proposed theories for the behavior. Here the layers of apple further into the “tuck” we will very briefly introduce one of the lower later. However, this phenomenon many theories proposed. was also observed in Co doped samples. Unlike Ru or Ir, Co has a slightly smaller One group suggested the radius than Fe, but the shrinking of state, arguing that versus doping is comparable with superconductivity in Fe-based those with Ru or Ir doping. superconductors is unconventional and mediated by anti-ferromagnetic spin fluctuations. The theory suggested that Figure 4 Observed (crosses) and calculated the superconductivity is induced by the (solid line) neutron diffraction intensities of nesting-related anti-ferromagnetic spin PrFeAsO at 175 K and 5K The 175K data was fluctuations near the wave vectors fitted with tetragonal structure with space group connecting the electron and hole pockets. P4/nmm, while the 5K data was fitted with [10, 14] Cmma. The inset on the left shows the detailed data for 18°<2θ<38°, where is no common consensus most of the observable magnetic peaks are among the scientific community on any located. Magnetic peaks can be seen in the 5K particular theory/ model for Fe-based data but not at 175K. The inset on the right shows the splitting of the 220 peak in the superconductors yet. tetragonal structure, indicating a structural phase transition between the two temperatures [5]. Theories Conclusion From an experimentalist point of The field of Fe-based view, it seems that the superconducting superconductors is new and exciting. ground state can be induced by There are new theories proposed for the suppressing the magnetic phase systems every month and new transition, which can be done in a discoveries that contradicts the theories
substitution of Fe atoms for those with larger radius would increases lattice parameter a and b, while decreases parameter c. Imagine having a network of closely packed oranges on one surface, with another layer of apples on top, by replacing the oranges with watermelons, one should be able to “tuck” the layers of apple further into the lower later. However, this phenomenon was also observed in Co doped samples. Unlike Ru or Ir, Co has a slightly smaller radius than Fe, but the shrinking of versus doping is comparable with those with Ru or Ir doping. Figure 4 Observed (crosses) and calculated (solid line) neutron diffraction intensities of PrFeAsO at 175 K and 5K The 175K data was fitted with tetragonal structure with space group P4/nmm, while the 5K data was fitted with Cmma. The inset on the left shows the detailed data for 18°<2θ<38°, where most of the observable magnetic peaks are located. Magnetic peaks can be seen in the 5K data but not at 175K. The inset on the right shows the splitting of the 220 peak in the tetragonal structure, indicating a structural phase transition between the two temperatures [5]. Theories From an experimentalist point of view, it seems that the superconducting ground state can be induced by suppressing the magnetic phase transition, which can be done in a various ways such as F-doping of oxygen or simply by creating oxygen deficiency [5]. This is however not always the case [11]. For those that superconducts after the structural and magnetic transitions are suppressed, there have been various proposed theories for the behavior. Here we will very briefly introduce one of the many theories proposed. One group suggested the state, arguing that superconductivity in Fe-based superconductors is unconventional and mediated by anti-ferromagnetic spin fluctuations. The theory suggested that the superconductivity is induced by the nesting-related anti-ferromagnetic spin fluctuations near the wave vectors connecting the electron and hole pockets. [10, 14] is no common consensus among the scientific community on any particular theory/ model for Fe-based superconductors yet. Conclusion The field of Fe-based superconductors is new and exciting. There are new theories proposed for the systems every month and new discoveries that contradicts the theories
Introduction_to_Fe-based_superconductors.docx