Single nonmagnetic impurity resonance in FeSe-based 122-type superconductors as a probe for pairing symmetry

摘要

We study the effect of a single nonmagnetic impurity in A _yFe_(2-x)Se_2 (A = K, Rb, or Cs) superconductors by considering various pairing states based on a three-orbital model consistent with the photoemission experiments. The local density of states on and near the impurity site has been calculated by solving the Bogoliubov-de Gennes equations self-consistently. The impurity-induced in-gap bound states are found only for attractive impurity scattering potential, as in the cases of doping of Co or Ni, which is characterized by the strong particle-hole asymmetry, in the nodeless d_x ~2-y~2 wave pairing state. This property may be used to probe the pairing symmetry of FeSe-based 122-type superconductors.