Interaction Effects on Quasiparticle Localization in Dirty Superconductors

TL;DR

This paper investigates how quasiparticle interactions influence their localization in dirty superconductors with broken time reversal symmetry, revealing conditions for stable metallic phases and classifying universality classes.

Contribution

It identifies the dominant interaction in class C systems and analyzes its effects using renormalization group methods, clarifying the role of symmetry breaking in localization.

Findings

Spin-spin triplet interaction is crucial in class C systems.

Zeeman coupling or full spin symmetry breaking makes interactions irrelevant.

A stable metallic phase exists in 2D for class D superconductors.

Abstract

We study how quasiparticle interactions affect their localization properties in dirty superconductors with broken time reversal symmetry -- for example in a magnetic field. For SU(2) spin-rotation invariant (class C) systems, the only important coupling is the spin-spin triplet interaction, which we study within a renormalization group approach. Either an additional Zeeman coupling or a complete breaking of spin rotation symmetry renders all interactions irrelevant. These two situations realize, respectively, the non-interacting unitary Anderson and the ``thermal'' (class D) universality class. Our results imply a stable metallic phase in 2D for class D. Experimental implications are discussed.