The Study Of Impurity-induced Resonance State In BiS₂-based Superconductors

Superconductivity has always been the focus in the field of condensed matter physics.The recent discovery of superconductivity in a new family of BiS2-based superconductors has attracted considerable attention due to its similarities to the cuprate-based and iron-based superconductors.Superconductivity was firstly found in Bi4O4S3,whose superconducting transition temperature is Tc = 4.5K,and later superconductivity was successively found in ReO1-xBiS2(Re = La,Nd,Ce and Pr)and Sr1-xLaxFBiS2,up to now,the highest superconducting transition temperature(Tc =10.6K)was found in LaO0.5F0.5BiS2.These findings indicate that BiS2-based superconductors may have a relatively high transition temperature.At present,superconducting pairing symmetry in BiS2-based superconductors is still under debate.Due to the absence of direct experimental evidences,the conventional s-wave,the extended s-wave and the dx2-y2-wave have been mentioned theoretically,and further theoretical research and experimental confirmation are urgently need.BiS2-based superconductors have a layered crystal structure,which is very similar to that of cuprate-based and iron-based superconductors.Band structure calculations show that there is a strong Fermi-surface nesting,and it is believed that superconductivity occurs with the Fermi-surface nesting.This paper,used local electronic structure around a single nonmagnetic impurity to probe the pairing symmetry in BiS2-based superconductors.Within the two-orbital model for BiS2-based superconductors,the Fermi surface topology is calculated by the first principles.Considering the pairing symmetry of the conventional s-wave,the extended s-wave,and the dx2-y2-wave with different doping in the case of weak scattering and strong scattering,T-matrix approach and Green's function were used to investigate the effect from a single nonmagnetic impurity scattering on impurity resonance states and spatial modulation structure.The results showed that the effect from a single nonmagnetic impurity scattering with the conventional s-wave,the extended s-wave,and the dx2-y2-wave symmetries may induce different resonance states and spatial modulation structures as a result of nodal structures on different Fermi surface topologies with different doping.We believed that these differences need to be confirmed by the scanning tunneling microscopy(STM)experiments,which provides a theoretical basis for the superconducting pairing symmetry,and it will help to reveal the unconventional superconducting mechanism in BiS2-based superconductors.