Multigap Superconductivity in Y2C3: A 13C-NMR Study

We report on the superconducting properties of Y₂C₃ with a relatively high transition temperature T_c = 15.7 K investigated by ¹³C nuclear-magnetic-resonance (NMR) measurements under a magnetic field. The ¹³C 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/T₁ in the superconducting state, Y₂C₃ is demonstrated to be a multigap superconductor that exhibits a large gap 2Δ/k_BT_c=5 at the main band and a small gap 2Δ/k_BT_c=2 at other bands. These results have revealed that Y₂C₃ is a unique multigap s-wave superconductor similar to MgB₂.