Statistics of subgap states in $s_\pm$ superconductors

TL;DR

This paper investigates the statistical properties of impurity-induced subgap states in $s_{}$ superconductors, revealing insights into localization, mobility edges, and limitations of common approximation methods.

Contribution

It provides a numerical analysis of subgap state statistics in $s_{}$ superconductors, including localization behavior and the inaccuracy of the self-consistent T-matrix approximation.

Findings

Identification of the mobility edge in 3D cases.

Crossover between weak and strong localization in 2D.

Self-consistent T-matrix approximation is not very accurate.

Abstract

There is strong support in favor of an unusual $s_{\pm}$ superconducting state in the new iron-based superconductors, in which the gap parameter has opposite signs in different bands. In this case scattering between different bands by impurities has a pair-breaking effect and introduces states inside the gap. We studied the statistics of disorder-induced subgap states in $s_{\pm}$ superconductors due to collective effects of impurities. Numerically solving the two-band Bogolyubov equations, we explored the behavior of the density of states and localization length. We located the mobility edge separating the localized and delocalized states for the 3D case and the crossover between the weak and strong localization regimes for the 2D case. We found that the widely used self-consistent T-matrix approximation is not very accurate in describing subgap states.