On the phonon-induced superconductivity of disordered alloys

TL;DR

This paper develops a theoretical model for alloy superconductivity considering both disorder effects and electron-phonon interactions, deriving equations to analyze how disorder influences the critical temperature and pairing mechanisms.

Contribution

It introduces a conserving approximation framework for alloy disorder and electron-phonon interactions, deriving Eliashberg-type equations and analyzing disorder effects on superconductivity.

Findings

Anderson's theorem holds when disorder renormalizations are neglected.

Disorder renormalization of electron-phonon interaction affects $T_c$ predictions.

Expressions for $T_c$ are provided for weak and intermediate coupling regimes.

Abstract

A model of alloy is considered which includes both quenched disorder in the electron subsystem (``alloy'' subsystem) and electron-phonon interaction. For given approximate solution for the alloy part of the problem, which is assumed to be conserving in Baym's sense, we construct the generating functional and derive the Eliashberg-type equations which are valid to the lowest order in the adiabatic parameter.The renormalization of bare electron-phonon interaction vertices by disorder is taken into account consistently with the approximation for the alloy self-energy. For the case of exact configurational averaging the same set of equations is established within the usual T-matrix approach. We demonstrate that for any conserving approximation for the alloy part of the self-energy the Anderson's theorem holds in the case of isotropic singlet pairing provided disorder renormalizations of the electron-phonon interaction vertices are neglected. Taking account of the disorder renormalization of the electron-phonon interaction we analyze general equations qualitatively and present the expressions for $T_{c}$ for the case of weak and intermediate electron-phonon coupling. Disorder renormalizations of the logarithmic corrections to the effective coupling, which arise when the effective interaction kernel for the Cooper channel has the second energy scale, as well as the renormalization of the dilute paramagnetic impurity suppression are discussed.