Two-Gap Time Reversal Symmetry Breaking Superconductivity in Non-Centrosymmetric LaNiC2

TL;DR

This study uses muon spin rotation to investigate LaNiC2, revealing two nodeless gaps and time-reversal symmetry breaking, indicating unconventional superconductivity with a specific pairing mechanism.

Contribution

First single-crystal muSR study of LaNiC2 that determines absolute penetration depth and vortex core size, confirming two-gap nodeless superconductivity and time-reversal symmetry breaking.

Findings

Presence of two nodeless superconducting gaps

Detection of weak internal magnetic fields indicating time-reversal symmetry breaking

Confirmation of interorbital equal-spin pairing in LaNiC2

Abstract

We report a $\mu$SR investigation of a non-centrosymmetric superconductor (LaNiC$_2$) in single crystal form. Compared to previous $\mu$SR studies of non-centrosymmetric superconducting polycrystalline and powder samples, the unambiguous orientation of single crystals enables a simultaneous determination of the absolute value of the magnetic penetration depth and the vortex core size from measurements that probe the magnetic field distribution in the vortex state. The magnetic field dependence of these quantities unambiguously demonstrates the presence of two nodeless superconducting energy gaps. In addition, we detect weak internal magnetic fields in the superconducting phase, confirming earlier $\mu$SR evidence for a time-reversal symmetry breaking superconducting state. Our results suggest that Cooper pairing in LaNiC$_2$ is characterized by the same interorbital equal-spin pairing model introduced to describe the pairing state in the centrosymmetric superconductor LaNiGa$_2$.