Impurity effect on Bogoliubov Fermi surfaces: Analysis based on iron-based superconductors

The effect of impurities on a superconductor with Bogoliubov Fermi surfaces (BFSs) is studied using a realistic tight -binding model. Based on the band structure composed of d -orbitals in tetragonal FeSe, whose S -doped sample is a potential material for a BFS, we construct the superconducting state by introducing a time -reversal broken pair potential in terms of the band index. We further consider the effect of impurities on the BFS, where the impurity potential is defined as a local potential for the original d -orbitals. The self -energy is calculated using the (self -consistent) Born approximation, which shows an enhancement of the single -particle spectral weight on the Fermi surface. This is consistent with the previous phenomenological theory and is justified by the present more detailed calculation based on the FeSe-based material.