Time-reversal symmetry breaking in UTe2

Topological superconductivity is a long-sought state of matter in bulk materials, and odd-parity superconductor UTe2 is a prime candidate. Several experiments provide evidence that the superconducting order parameter in UTe2 is multicomponent and breaks time-reversal symmetry. Because UTe2 has orthorhombic symmetry, proposals for its superconducting order parameter involve two nearly-degenerate irreducible representations (e.g., B2u + iB3u). By applying symmetry-breaking uniaxial strain, we probe multicomponent superconductivity by looking for a splitting of the transition temperatures. Our findings do not reveal any evidence for two nearly-degenerate order parameters near ambient pressure. Next, we performed Kerr effect measurements on a number of UTe2 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. Finally, usr measurements on a sample grown via molten-salt-flux also show no evidence for time-reversal symmetry breaking in the superconducting state. These results imply that the superconducting state of UTe2 does not intrinsically break time-reversal symmetry.