Disorder induced transition between s_+- and s_++ states in two-band superconductors

TL;DR

This paper investigates how disorder affects two-band superconductors, revealing a transition from s_{±} to s_{++} states driven by impurity scattering, with implications for experimental observations.

Contribution

The study demonstrates a disorder-induced transition between s_{±} and s_{++} states using the T-matrix approximation, highlighting the robustness of T_c and the role of the average coupling constant.

Findings

T_c suppression depends on a single impurity scattering parameter.

Disorder induces a transition from s_{±} to s_{++} states.

T_c is more robust against nonmagnetic impurities than traditional theories suggest.

Abstract

We have reexamined the problem of disorder in two-band superconductors, and shown within the framework of the T-matrix approximation, that the suppression of T_c can be described by a single parameter depending on the intraband and interband impurity scattering rates. T_c is shown to be more robust against nonmagnetic impurities than would be predicted in the trivial extension of Abrikosov-Gor'kov theory. We find a disorder-induced transition from the s_{\pm} state to a gapless and then to a fully gapped s_{++} state, controlled by a single parameter -- the sign of the average coupling constant <\lambda> . We argue that this transition has strong implications for experiments.