Magnetic response of noncentrosymmetric superconductor La2C3: Effect of double-gap and spin-orbit interaction

The presence of spin-orbit (SO) interaction in a noncentrosymmetric superconductor, La2C3 (Tc≅11K) is demonstrated by muon spin rotation (μSR) in its normal state, where μSR spectra exhibit field-induced weak depolarization due to van Vleck-like local susceptibility. In the mixed state, muon spin relaxation due to inhomogeneity of internal field (σv) exhibits a field dependence that is characterized by a kink, where σv (and hence the superfluid density) is more strongly reduced at lower fields. This is perfectly in line with the presence of a secondary energy gap previously inferred from the temperature dependence of σv, and also consistent with the possible influence of asymmetric deformation of the Fermi surface due to the SO interaction.