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Evidence of nodal gap structure in the non-centrosymmetric superconductor Y2C3

The magnetic penetration depth $λ(T)$ and the upper critical field $% μ_{0}H_{c2}(T_{c})$ of the non-centrosymmetric (NCS) superconductor Y$_{2} $C$_{3}$ have been measured using a tunnel-diode (TDO) based resonant oscillation technique. We found that the penetration depth $λ(T)$ and its corresponding superfluid density $ρ_{s}(T)$ show linear temperature dependence at very low temperatures ($T\ll T_{c}$), indicating the existence of line nodes in the superconducting energy gap. Moreover, the upper critical field $μ_{0}H_{c2}(T_{c})$ presents an upturn at low temperatures with a rather high value of $μ_{0}H_{c2}(0)$ $\simeq 29$T, which slightly exceeds the weak-coupling Pauli limit. We discuss the possible origins for these nontrivial superconducting properties, and argue that the nodal gap structure in Y$_{2}$C$_{3}$ is likely attributed to the absence of inversion symmetry, which allows the admixture of spin-singlet and spin-triplet pairing states.