Two-Gap Time Reversal Symmetry Breaking Superconductivity in Non-Centrosymmetric LaNiC2
Abstract
We report a μSR investigation of a non-centrosymmetric superconductor (LaNiC2) in single crystal form. Compared to previous μSR 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 μSR evidence for a time-reversal symmetry breaking superconducting state. Our results suggest that Cooper pairing in LaNiC2 is characterized by the same interorbital equal-spin pairing model introduced to describe the pairing state in the centrosymmetric superconductor LaNiGa2.