Multigap superconductivity in Y2C3:: A 13C-NMR study

We report on the superconducting properties of Y2C3 with a relatively high transition temperature T-c = 15.7K investigated by C-13 nuclear-magnetic-resonance (NMR) measurements under a magnetic field. The C-13 Knight shift has revealed a significant decrease below Tc, suggesting a spin-singlet superconductivity. From an analysis of the temperature dependence of the nuclear spin-lattice relaxation rate 1/T-1 in the superconducting state, Y2C3 is demonstrated to be a multigap superconductor that exhibits a large gap 2 Delta/k(B)T(c) = 5 at the main baud and a small gap 2 Delta/k(B)T(c) = 2 at other bands. These results have revealed that Y2C3 is a unique multigap s-wave superconductor similar to MgB2.