Tunneling spectra of impurity states in unconventional superconductors

We investigate the role of Bloch functions and superconducting gap symmetries on formation properties impurity-induced resonances in a two-dimensional superconductor, elucidate their manifestation scanning tunneling spectra. use extend recently developed scattering approach, conveniently formulating results terms phase shifts electron off impurity. find that discrete subgap states nodeless-gap superconductor are insensitive to potential shift (common for two spin species) if time-reversal symmetry (TRS) is preserved. The independence exact $s$-wave superconductors. It remains an accurate approximation over broad range energies when function breaks lattice point symmetry, except narrow region below edge. Breaking TRS makes capable creating spin-degenerate states, which may be further split by spin-dependent scattering. In nodal-gap superconductors, broadened coupling quasiparticle continuum. identify conditions allowing resonances. addition finding energy spectrum, we evaluate spin-resolved differential conductance all considered structures.