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Fei Chen 1 , Bo Zhou 1 , Yan Zhang 1 , Jia Wei 1 , Hong-Wei Ou 1 , Jia-Feng Zhao 1 , 1 1 2 2 

# Electronic structure of Fe 1$_{.}$04 (Te 0$_{.}$66 Se 0$_{.}$34 ) 

Cheng He , Qing-Qin Ge , Masashi Arita , Kenya Shimada , Hirofumi Namatame 2 , 2 3 4 5 1$_{∗}$ 

Masaki Taniguchi , Zhong-Yi Lu , Jiangping Hu , Xiao-Yu Cui , D. L. Feng 

$^{1}$Department of Physics, Surface Physics Laboratory (National Key Laboratory), and Advanced Materials Laboratory, Fudan University, Shanghai 200433, P. R. China 

$^{2}$Hiroshima Synchrotron Radiation Center and Graduate School of Science, Hiroshima University, Hiroshima 739-8526, Japan. 

$^{3}$Department of Physics, Renmin University of China, Beijing 100872, P. R. China 4 

Department of Physics, Purdue University, West Lafayette, IN 47907, USA and 5 

Swiss Light Source, Paul-Scherrer Institut, 5232 Villigen, Switzerland 

(Dated: October 31, 2018) 

We report the electronic structure of the iron-chalcogenide superconductor, Fe 1 . 04 (Te 0 . 66 Se 0 . 34 ), obtained with high resolution angle-resolved photoemission spectroscopy and density functional cal- culations. In photoemission measurements, various photon energies and polarizations are exploited to study the Fermi surface topology and symmetry properties of the bands. The measured band structure and their symmetry characters qualitatively agree with our density function theory calcu- lations of Fe(Te 0 . 66 Se 0 . 34 ), although the band structure is renormalized by about a factor of three. We find that the electronic structures of this iron-chalcogenides and the iron-pnictides have many aspects in common, however, significant differences exist near the Γ -point. For Fe 1 . 04 (Te 0 . 66 Se 0 . 34 ), there are clearly separated three bands with distinct even or odd symmetry that cross the Fermi en- ergy ( E$_{F}$ ) near the zone center, which contribute to three hole-like Fermi surfaces. Especially, both experiments and calculations show a hole-like elliptical Fermi surface at the zone center. Moreover, no sign of spin density wave was observed in the electronic structure and susceptibility measurements of this compound. 

The discovery of superconductivity with the super- conducting transition temperature ( T$_{c}$ ) up to 55 K in iron-pnictides [1–3] has generated great interests. The FeAs layer is considered as the key structure for super- conductivity in systems ranging from SmO 1$_{−}$ $_{x}$F$_{x}$ FeAs, Ba 1$_{−}$ $_{x}$K$_{x}$ Fe 2 As 2 [4, 5], to LiFeAs [6, 7]. Recently, certain iron-chalcogenides, eg. Fe 1+ $_{x}$Se, Fe 1+ $_{y}$Te 1$_{−}$ $_{x}$Se$_{x}$ [8, 9], have been found to be superconducting as well. Fe 1+ $_{x}$Se shows superconductivity at 8 K under ambient pres- sure [8] and 37 K under a 7 GPa hydrostatic pressure [10], which is comparable to Ba 1$_{−}$ $_{x}$K$_{x}$ Fe 2 As 2 (T$_{c}$=38 K) [5]. Because iron-chalcogenides do not involve arsenic, it would be particularly important for applications. Fur- thermore, although Fe 3 d orbitals play a vital role in the iron-based high temperature superconductors, the anions seem also play an important role on various aspects, not- ing LaOFeP possesses a T$_{c}$ of merely 5 K. Besides the size effect, the polarizability of the anions has even been suggested to be crucial for the superconductivity [11]. Therefore, iron-chalcogenides provide an opportunity to study the role of anions in iron-based superconductors. 

The iron-pnictides and iron-chalcogenides have many things in common. The FeSe(Te) layer in Fe 1+ $_{y}$Te 1$_{−}$ $_{x}$Se$_{x}$ is isostructural to the FeAs or FeP layer in iron-pnictides. Moreover, the phase diagram of Fe 1+ $_{y}$Te 1$_{−}$ $_{x}$Se$_{x}$ resem- 

## I. INTRODUCTION 

bles that of the iron-pnictides, where the competition between magnetism and superconductivity has been ob- served in both cases. The undoped Fe 1+ $_{y}$Te exhibits a spin density wave (SDW) ground state. With sufficient selenium doping, the SDW is suppressed, and the super- conductivity occurs at a T$_{c}$ as high as 15 K [9]. 

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