The fate of time-reversal symmetry breaking in UTe2

TL;DR

This study investigates whether the superconducting state of UTe$_2$ intrinsically breaks time-reversal symmetry by measuring Kerr effects, finding no evidence of spontaneous symmetry breaking in various samples.

Contribution

The paper provides the first systematic Kerr effect measurements on multiple UTe$_2$ samples, challenging previous claims of intrinsic time-reversal symmetry breaking in this material.

Findings

No spontaneous Kerr signal in zero field measurements.

Field-trainable Kerr signals indicate inhomogeneous magnetic regions.

Results constrain the possible superconducting order parameters of UTe$_2$.

Abstract

Topological superconductivity is a long-sought state of matter in bulk materials, and odd-parity superconductor UTe$_2$ is a prime candidate. The recent observation of a field-trainable spontaneous Kerr signal in UTe$_2$ at the onset of superconductivity provides strong evidence that the superconducting order parameter is multicomponent and breaks time-reversal symmetry. Here, we perform Kerr effect measurements on a number of UTe$_2$ samples -- grown $via$ both chemical vapor transport and the molten-salt-flux methods -- that show a single superconducting transition between 1.6~K and 2.1~K. Our results show no evidence for a spontaneous Kerr signal in zero field measurements. This implies that the superconducting state of UTe$_2$ does not intrinsically break time-reversal symmetry. Instead, we observe a field-trainable signal that varies in magnitude between samples and between different locations on a single sample, which is a sign of inhomogeneous magnetic regions. Our results provide an examination of representative UTe$_2$ samples and place strong constraints on the superconducting order parameter of UTe$_2$.