Non-magnetic impurity effects in a three-dimensional topological superconductor: From p- to s-wave behaviors

Unconventional features in superconductivity are revealed by responses to impurity scattering. We study non-magnetic impurity effects in a three-dimensional topological superconductor, focusing on an effective model (massive Dirac Hamiltonian with s-wave on-site pairing) of Copper-doped bismuth-selenium compounds. Using a self-consistent T-matrix approach for impurity scattering, we examine in-gap states in density of states. We find that the results are well characterized by a single material variable, which measures relativistic effects in the Dirac Hamiltonian. In non-relativistic regime, an odd-parity superconducting state is fragile against non-magnetic impurities. We show that this behavior is caused by a p-wave character involved in the topological superconducting state. In contrast, we show that in relativistic regime the superconductivity is robust against non-magnetic impurities, owing to an s-wave character. To summarize, the system has two aspects, p- and s-wave features, depending on the weight of relativistic effects.