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abstract: 'In this work, we study the [A$_{x}$Fe$_{2-y}$Se$_2$]{} (A=K, Rb) superconductors using angle-resolved photoemission spectroscopy. In the low temperature state, we observe an orbital-dependent renormalization for the bands near the Fermi level in which the [$d_{xy}$]{} bands are heavily renormliazed compared to the [$d_{xz}$/$d_{yz}$]{} bands. Upon increasing temperature to above 150K, the system evolves into a state in which the [$d_{xy}$]{} bands have diminished spectral weight while the [$d_{xz}$/$d_{yz}$]{} bands remain metallic. Combined with theoretical calculations, our observations can be consistently understood as a temperature induced crossover from a metallic state at low temperature to an orbital-selective Mott phase (OSMP) at high temperatures. Furthermore, the fact that the superconducting state of [A$_{x}$Fe$_{2-y}$Se$_2$]{} is near the boundary of such an OSMP constraints the system to have sufficiently strong on-site Coulomb interactions and Hund’s coupling, and hence highlight the non-trivial role of electron correlation in this family of iron superconductors.'
author:
- 'M. Yi'
- 'D.H. Lu'
- 'R. Yu'
- 'S. C. Riggs'
- 'J.-H. Chu'
- 'B. Lv'
- 'Z. Liu'
- 'M. Lu'
- 'Y.-T. Cui'
- 'M. Hashimoto'
- 'S.-K. Mo'
- 'Z. Hussain'
- 'C. W. Chu'
- 'I.R. Fisher'
- 'Q. Si'
- 'Z.-X. Shen'
