M. Yi, Z.K. Liu, Y. Zhang, M. Wang, R. Yu, J.-X. Zhu, A. Kemper, J.J. Lee, R.G. Moore, C. Riggs, J.-H. Chu, B. Lv, J. Hu

UC Berkeley

Understanding superconductivity in iron chalcogenide materials is an important focus in the current study of iron-based superconductors. In particular, the lack of hole Fermi pockets at the Brillouin zone center put serious doubt on the previous proposal of spin fluctuation mediated pairing via Fermi surface nesting. Using angle-resolved photoemission spectroscopy (ARPES) we studied different families of iron chalcogenide superconductors.

Our results show that instead of Fermi surface topology, strong electron correlation is an important ingredient for superconductivity in the iron chalcogenides. Specifically, i) there exists universal strong orbital-selective renormalization effects and proximity to an orbital-selective Mott phase in Fe(Te,Se), A_xFe_2-ySe₂ (A = alkali metal), and monolayer FeSe film on STO, and ii) in Rb_xFe_2-y(Se,S)₂, where sulfur substitution for selenium continuously suppresses superconductivity down to zero, little change occurs in the Fermi surface topology, but a substantial reduction of electron correlation is observed in the overall bandwidth, implying that electron correlation is the tuning parameter for superconductivity in this material.