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

TL;DR

This study investigates how a single non-magnetic impurity affects the local electronic states in FeSe-based 122-type superconductors, providing insights into their pairing symmetry through impurity-induced bound states.

Contribution

It introduces a theoretical analysis of impurity effects using a three-orbital model to identify signatures of pairing symmetry in FeSe-based superconductors.

Findings

In-gap bound states occur only with attractive impurity potential.

Strong particle-hole asymmetry is observed in the bound states.

The results suggest a way to probe pairing symmetry in these materials.

Abstract

We study the effect of a single non-magnetic impurity in A$_{y}$Fe$_{2-x}$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.