Impurities with retarded interaction with quasiparticles in a s-wave superconductor

TL;DR

This paper develops a perturbation theory for quasiparticle scattering with retarded interactions in disordered s-wave superconductors, revealing that impurities can enhance the critical temperature due to nonelastic scattering effects.

Contribution

It introduces a generalized perturbation theory and Eliashberg equations for disordered superconductors with retarded impurity interactions, showing violation of Anderson's theorem.

Findings

Impurities can increase the critical temperature of s-wave superconductors.

Nonelastic scattering effects amplify superconducting properties.

The theory extends existing models to include retarded impurity interactions.

Abstract

A perturbation theory and a diagram technique for a disordered metal are proposed when scattering of quasiparticles by nonmagnetic impurities is caused with a retarded interaction. The perturbation theory generalizes a case of the elastic scattering in a disordered metal. Eliashberg equations for s-wave superconductivity are generalized for such a disordered superconductor. Anderson's theorem is found to be violated in the sense that embedding of the impurities into a s-wave superconductor increases its critical temperature. We showed the amplification of superconducting properties is a result of nonelastic effects in a scattering by the impurities.