Multigap Superconductivity in Y$_2$C$_3$: A $^{13}$C-NMR Study

We report on the superconducting (SC) properties of Y 2 C 3 with a relatively high transition temperature T c = 15 . 7 K investigated by 13 C nuclear-magnetic-resonance (NMR) measurements under a magnetic field. The 13 C Knight shift has revealed a significant decrease below T c , suggesting a spin-singlet superconductivity. From an analysis of the temperature dependence of the nuclear spin-lattice relaxation rate 1 /T 1 in the SC state, Y 2 C 3 is demonstrated to be a multigap superconductor that exhibits a large gap 2∆ /k B T c = 5 at the main band and a small gap 2∆ /k B T c = 2 at other bands. These results have revealed that Y 2 C 3 is a unique multigap s-wave superconductor similar to MgB 2 .