Ward identities for disordered metals and superconductors

TL;DR

This paper revisits Ward identities in disordered metals and superconductors, providing a simplified derivation rooted in gauge invariance and reformulating the identities to analyze quasiparticle charge conservation or non-conservation.

Contribution

It introduces a new, simplified derivation of Ward identities for disordered metals and superconductors based on gauge invariance, enabling easier analysis of charge conservation properties.

Findings

Reformulated Ward identities for disordered systems

Analysis of quasiparticle charge conservation in different materials

Simplified derivation method based on gauge invariance

Abstract

This article revisits Ward identities for disordered interacting normal metals and superconductors. It offers a simple derivation based on gauge invariance and recasts the identities in a new form that allows easy analysis of the quasiparticle charge conservation (as e.g. in a normal metal) or non-conservation (as e.g. in a d-wave superconductor).