Supercurrents and spontaneous time-reversal symmetry breaking by nonmagnetic disorder in unconventional superconductors

TL;DR

This paper investigates how nonmagnetic disorder in unconventional superconductors can induce local orbital currents through local extended s-wave pairing, leading to spontaneous time-reversal symmetry breaking.

Contribution

It reveals that disorder-induced orbital currents originate from local extended s-wave pairing and discusses the energetics of regions with s±id order supporting spontaneous currents.

Findings

Disorder can induce local orbital currents in d-wave superconductors.

Local extended s-wave pairing explains the emergence of these currents.

Regions with s±id order support spontaneous local currents.

Abstract

Recently, a theoretical study [Li {\it et al.},~npj Quantum Materials 6, 36 (2021)] investigated a model of a disordered $d$-wave superconductor, and reported local time-reversal symmetry breaking current loops for sufficiently high disorder levels. Since the pure $d$-wave superconducting state does not break time-reversal symmetry, it is surprising that such persistent currents arise purely from nonmagnetic disorder. Here we perform a detailed theoretical investigation of such disorder-induced orbital currents, and show that the occurrence of the currents can be traced to local extended $s$-wave pairing. We discuss the energetics leading to regions of $s\pm id$ order, which support spontaneous local currents in the presence of inhomogeneous density modulations.