Magnetic pair breaking in disordered superconducting films

TL;DR

This paper develops a strong-coupling theory to analyze how nonmagnetic disorder influences magnetic pair breaking in disordered superconducting films, revealing a weak dependence consistent with experimental observations.

Contribution

It introduces a theoretical framework that accounts for disorder effects on pair breaking rate, highlighting the cancellation between electron-phonon enhancement and spin-flip scattering.

Findings

Weak dependence of pair breaking rate on disorder for certain resistances

Agreement with recent experimental results

Disorder effects tend to cancel each other in pair breaking

Abstract

A theory for the effects of nonmagnetic disorder on the magnetic pair breaking rate $\alpha$ induced by paramagnetic impurities in quasi two-dimensional superconductors is presented. Within the framework of a strong-coupling theory for disordered superconductors, we find that the disorder dependence of $\alpha$ is determined by the disorder enhancements of both the electron-phonon coupling and the spin-flip scattering rate. These two effects have a tendency to cancel each other. With parameter values appropriate for Pb_{0.9} Bi_{0.1}, we find a pair breaking rate that is very weakly dependent on disorder for sheet resistances 0 < R < 2.5 kOhm, in agreement with a recent experiment by Chervenak and Valles.