Orbital-selectivity in iron chalcogenide superconductors

The electron correlation strength has a systematic spread across the material-base of iron-based superconductors. Near the most correlated end of the spectrum are the iron chalcogenides, where strong orbital-selective correlations are observed. In particular, the dxy orbital exhibits much stronger local behavior than the dxz and dyz orbitals, putting the material in close proximity to an orbital-selective Mott phase (OSMP). In this talk, I will first demonstrate the universality of orbital-selectivity amongst all iron chalcogenide superconductors including both Fe(Te,Se) and heavily electron-doped FeSe systems. For the second part of the talk, I will use the phase diagram of Fe(Te,Se) to illustrate that both Te-substitution and temperature increase act as effective pathways towards the OSMP. In the process, a dramatic increase of the dxy effective mass together with a redistribution of spectral weight on the Fermi surface strongly modify the low energy electronic states of this material family.