Using angle-resolved photoemission spectroscopy, we observe the low-temperature state of the AxFe2-ySe2 (A=K, Rb) superconductors to exhibit an orbital-dependent renormalization of the bands near the Fermi level - the dxy bands heavily renormalized compared to the dxz/dyz bands. Upon raising the temperature to above 150 K, the system evolves into a state in which the dxy bands have depleted spectral weight while the dxz/dyz bands remain metallic. Combined with theoretical calculations, our observations can be consistently understood as a temperature-induced crossover from a metallic state at low temperatures to an orbital-selective Mott phase at high temperatures. Moreover, the fact that the superconducting state of A xFe2-ySe2 is near the boundary of such an orbital-selective Mott phase constrains the system to have sufficiently strong on-site Coulomb interactions and Hund's coupling, highlighting the nontrivial role of electron correlation in this family of iron-based superconductors.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)