Inhomogeneous time-reversal symmetry breaking in $\mathrm{Sr}_{2}\mathrm{Ru}\mathrm{O}_{4}$

TL;DR

This paper explains the observed local time-reversal symmetry breaking in Sr₂RuO₄ as caused by inhomogeneous strain fields near dislocations, leading to a mixed pairing state and a sharp transition without a heat capacity anomaly.

Contribution

It introduces a model where strain inhomogeneities induce local TRSB in Sr₂RuO₄, providing a unified explanation for experimental observations.

Findings

TRSB arises from inhomogeneous strain near dislocations.

The transition occurs without a detectable heat capacity anomaly.

Plastic deformation can control the onset of TRSB.

Abstract

We show that the observed time-reversal symmetry breaking (TRSB) of the superconducting state in $\mathrm{Sr}_{2}\mathrm{Ru}\mathrm{O}_{4}$ can be understood as originating from inhomogeneous strain fields near edge dislocations of the crystal. Specifically, we argue that, without strain inhomogeneities, $\mathrm{Sr}_{2}\mathrm{Ru}\mathrm{O}_{4}$ is a single-component, time-reversal symmetric superconductor, likely with $d_{x^{2}-y^{2}}$ symmetry. However, due to the strong strain inhomogeneities generated by dislocations, a slowly-decaying sub-leading pairing state contributes to the condensate in significant portions of the sample. As it phase winds around the dislocation, time-reversal symmetry is locally broken. Global phase locking and TRSB occur at a sharp Ising transition that is not accompanied by a change of the single-particle gap and yields a very small heat capacity anomaly. Our model thus explains the puzzling absence of a measurable heat capacity anomaly at the TRSB transition in strained samples, and the dilute nature of the time-reversal symmetry broken state probed by muon spin rotation experiments. We propose that plastic deformations of the material may be used to manipulate the onset of broken time-reversal symmetry.