Study On The Local Electronic Structure In BiS₂-based Superconducting Materials

Since the earliest metal mercury reached superconductivity at very low temperatures,many new members have gradually added to the superconductor family,such as organic superconductors,ceramic high-temperature superconductors,Y-B-C-O high-temperature superconductors,iron-based superconductors,magnesium boride superconductors,etc.which promoted the development of the superconducting field.In 2012,Japanese scientists Mizuguchi Y.and others reported the superconductivity of the Bi₄O₄S₃and La O₁–_xF_xBiS₂.Subsequently,the number of members of the BiS₂-based superconductor family was increasing.Scientists have also carried out comprehensive experimental research on this superconducting family,include conducted research on superconducting transition temperature,magnetic susceptibility,atomic lattice structure and other aspects of various samples of different types and different compositions.But so far,the superconducting pairing symmetry of this new material is still controversial.Due to the lack of direct experimental evidence,d_x²-_y²-wave,extended s-wave and traditional s-wave that mentioned theoretically have been studied by scholars,but the superconducting pair symmetry requires further experimental exploration to confirm.In superconductors,a crucial requirement is to confirm the pairing symmetry of the superconducting（SC）state,which may help to reveal the underlying SC mechanism.In this paper,we use the method of impurity scattering to study the pairing symmetry of BiS₂-based superconducting materials.By establishing a Hamiltonian model,useing the Green’s function and T-matrix approximation,we fitted the energy scattering on a two-dimensional plane and the topological structure of the Fermi surface,theoretically calculated the local electronic structure under the conditions of a single magnetic impurity doping at different concentrations.In order to further verify and ensure the accuracy of the calculation,the electronic structure evolution is also calculated.Considering d_x²-_y²-wave,extended s-wave,and traditional s-wave,the study found that a single magnetic impurity scattering will cause different resonance states of the impurities for different pairing symmetry,and the external manifestation is different in the local electronic structure and electronic structure evolution.The change of impurity concentration will also affect the resonance state.Comparative analysis shows that due to the different doping concentration,the cutting state of the energy gap cut-off line and the Fermi surface is different,and the resonance state of the impurities also shows a significant difference.Through directly verify of the resonance state caused by impurities,we can judge the SC pairing symmetry in the BiS₂-based superconductor,provide theoretical basis for revealing the unconventional superconducting mechanism of BiS₂-based superconductors.