Qian-En Wang, Zi-Jian Yao, Fu-Chun Zhang
The effect of a single nonmagnetic impurity in A$_{y}$Fe$_{2-x}$Se$_{2}$ (A=K, Rb, or Cs) superconductors has been studied based on a three-orbital model. The local density of states on and near the impurity site has been calculated by solving the Bogoliubov-de Gennes equations self-consistently. Both repulsive and attractive impurity scattering potential are considered in our calculations. The impurity-induced in-gap bound states are found only for attractive scattering potential in the state of $d_{x^2-y^2}$ wave pairing, and it turns out that they are very sensitive to the magnitude of the scattering potential. The emergence of the impurity-induced bound states in the vicinity of the Fermi level demonstrates a strong violation of the electron-hole symmetry which is originated from the nodeless $d_{x^2-y^2}$ wave pairing state. The results obtained in our calculation, which simulate the doping of Co and Ni in FeSe-based 122-type superconductors, as an approach to examine the pairing symmetry of this novel superconducting material, can be a proposal of STM observation.
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http://arxiv.org/abs/1208.4917
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