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Open Access Publications from the University of California

Electronic structure and spatial inhomogeneity of iron-based superconductor FeS**Project supported by CAS-Shanghai Science Research Center, China (Grant No. CAS-SSRC-YH-2015-01), the National Key R&D Program of China (Grant No. 2017YFA0305400), the National Natural Science Foundation of China (Grant Nos. 11674229, 11227902, and 11604207), the EPSRC Platform Grant (Grant No. EP/M020517/1), Hefei Science Center, Chinese Academy of Sciences (Grant No. 2015HSC-UE013), Science and Technology Commission of Shanghai Municipality, China (Grant No. 14520722100), and the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (Grant No. XDB04040200).


Iron-based superconductor family FeX (X = S, Se, Te) has been one of the research foci in physics and material science due to their record-breaking superconducting temperature (FeSe film) and rich physical phenomena. Recently, FeS, the least studied FeX compound (due to the difficulty in synthesizing high quality macroscopic crystals) attracted much attention because of its puzzling superconducting pairing symmetry. In this work, combining scanning tunneling microscopy and angle resolved photoemission spectroscopy (ARPES) with sub-micron spatial resolution, we investigate the intrinsic electronic structures of superconducting FeS from individual single crystalline domains. Unlike FeTe or FeSe, FeS remains identical tetragonal structure from room temperature down to 5 K, and the band structures observed can be well reproduced by our ab-initio calculations. Remarkably, mixed with the 1 × 1 tetragonal metallic phase, we also observe the coexistence of reconstructed insulating phase in the crystal, which not only helps explain the unusual properties of FeS, but also demonstrates the importance of using spatially resolved experimental tools in the study of this compound.

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