Abstract
We study the effect of a single non-magnetic impurity and vortex core states in iron-selenide superconductors by solving the Bogoliubov-de Gennes equations self-consistently based on a three-orbital model. The impurity-induced 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-wave pairing state. This property may be used to probe the pairing symmetry of iron-selenide 122-type superconductors. The orbital-resolved vortex core states are classified by the invariant subgroups of the symmetry group of the mean-field Hamiltonian in the presence of magnetic field. Numerical calculations show that isotropic s- and anisotropic s-wave vortices have G5 symmetry for each orbital, whereas d-wave vortices show G*6 symmetry for dxz/yz orbitals and G*5 symmetry for dxy orbital. Such orbital-resolved vortices differ by a relative phase due to hybridized-pairing between dxz and dyz orbitals which is essentially caused by a transformation of co-representation of G*5 and G*6 subgroups. The phase difference of orbital-resolved d-wave vortices can be verified by further experiment observation.