Anomalous momentum dependence of the multiband electronic structure of FeSe_1-xTe_x Superconductors induced by atomic disorder

When periodicity of crystal is disturbed by atomic disorder, its electronic state tends to be inhomogeneous and band dispersion is expected to be obscured. In case of Fe-based superconductors, disorder of chalcogen/pnictogen height is known to cause disorder of Fe 3d level splitting. Here, we report an angle-resolved photoemission spectroscopy study on FeSe_1-xTe _x with the chalcogen height disorder, showing that the disorder affects the Fe 3d band dispersions in an orbital-selective way instead of simple obscuring effect. The reverse of the Fe 3d level splitting due to the chalcogen height difference causes the splitting of the hole band with Fe 3d _x²-y² character around the Γ point.