We report on the superconducting (SC) properties of Y2C3 with a relatively high transition temperature Tc = 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 Tc, suggesting a spin-singlet superconductivity. From an analysis of the temperature dependence of the nuclear spin-lattice relaxation rate 1/T1 in the SC state, Y2C3 is demonstrated to be a multigap superconductor that exhibits a large gap 2∆/kBTc = 5 at the main band and a small gap 2∆/kBTc = 2 at other bands. These results have revealed that Y2C3 is a unique multigap s-wave superconductor similar to MgB2.KEYWORDS: lanthanoid carbide, metal, superconductivity, multigap, NMR, Y2C3The discovery of superconductivity in MgB 2 , which exhibits a high superconducting (SC) transition temperature T c ∼ 40 K, has attracted much interest.1 Motivated by this discovery, intensive effort is devoted to the search for a new high-T c material in a similar system that contains light elements B and C. Meanwhile, Amano et al. reported that Y 2 C 3 prepared under high pressure (∼ 5 GPa) is a superconductor with a relatively high T c ∼ 18 K, 2 although the superconductivity in this compound was already reported to emerge at T c ∼ 6−11 K.3 As for SC characteristics, the specific heat measurements on the newly synthesized high-purity samples of Y 2 C 3 have revealed that a gap size of the respective samples with T c = 11.6, 13.6, and 15.2 K increases as 2∆/k B T c =3.6, 4.1, and 4.4.4 This result raises a question why T c and 2∆/k B T c vary significantly depending on sintering conditions. Further systematic experiments are required to gain deep insight into the SC characteristics of this compound.Y 2 C 3 crystallizes in the cubic Pu 2 C 3 -type structure (space group I43d) without an inversion center, consisting of the dimers of carbon atoms. The SC properties of the sample previously reported by Amano et al. did not exhibit a single SC transition as seen in the inset of Fig. 1(a), pointing to a contamination of extrinsic multiple phases.2 Recently, Akutagawa et al. have succeeded in preparing a single phase of Y 2 C 3 , which enables us to extract intrinsic electronic and SC properties in Y 2 C 3 . From the specific-heat measurements of this sample, the Sommerfeld coefficient γ ∼ 6.3 mJ/mol·K 2 and Debye temperature θ D ∼ 530 K were estimated for the sample with T c = 15.2 K.4 This result suggests that its high Debye temperature makes T c relatively high despite its small Sommerfeld coefficient. As in MgB 2 , the lightelement constituent like boron and carbon plays a vital role in enhancing T c in general. In the SC state, the temperature (T ) dependence of the specific heat exhibits an exponential decrease with 2∆/k B T c = 4.4 upon cooling well below T c , suggesting a strong-coupling isotropic su- * E-mail address: aharada@nmr.mp.es.osaka-u.ac.jp perconductivity. From an other context, it is noteworthy that a novel SC nature for CePt 3 Si and Li 2 Pt 3 B without ...