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

TL;DR

This study provides evidence for line nodes in the superconducting gap of Y2C3, a non-centrosymmetric superconductor, through measurements of penetration depth and upper critical field, suggesting mixed pairing states due to lack of inversion symmetry.

Contribution

First to report the nodal gap structure in Y2C3, linking non-centrosymmetry to unconventional superconducting properties and mixed pairing states.

Findings

Linear temperature dependence of penetration depth indicates line nodes.

Upper critical field exceeds Pauli limit at low temperatures.

Nodal gap structure likely due to absence of inversion symmetry.

Abstract

The magnetic penetration depth $\lambda (T)$ and the upper critical field $% \mu_{0}H_{c2}(T_{c})$ 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 $\lambda (T)$ and its corresponding superfluid density $\rho_{s}(T)$ 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 $\mu_{0}H_{c2}(T_{c})$ presents an upturn at low temperatures with a rather high value of $\mu_{0}H_{c2}(0)$ $\simeq 29$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.