Effect of spatial variations of superconducting gap on suppression of the transition temperature by impurities

TL;DR

This paper investigates how local variations in the superconducting gap caused by impurities affect the critical temperature, revealing that such variations can reduce pair-breaking effects and potentially increase T_c in s-wave superconductors.

Contribution

It introduces a calculation of the correction to T_c due to spatial gap variations near impurities, highlighting effects in short-coherence length superconductors.

Findings

Local gap variations can significantly modify T_c in dirty superconductors.

Spatial inhomogeneities tend to reduce pair-breaking effects.

Nonmagnetic impurities may increase T_c in s-wave superconductors.

Abstract

We calculate correction to the critical temperature of a dirty superconductor, which results from the local variations of the gap function near impurity sites. This correction is of the order of T_c/E_F and becomes important for short-coherence length superconductors. It generally reduces a pair-breaking effect. In s-wave superconductors small amounts of nonmagnetic impurities can increase the transition temperature.