Multigap superconductivity in sesquicarbides La$_2$C$_3$ and Y$_2$C$_3$

TL;DR

This study reveals multigap, nodeless superconductivity in La$_2$C$_3$ and Y$_2$C$_3$ sesquicarbides through muon spin relaxation measurements, highlighting differences in interband coupling despite similar gap magnitudes.

Contribution

It demonstrates the complex multigap structure of the superconducting order parameter in these compounds using $bc$SR, providing new insights into their pairing mechanisms.

Findings

Both compounds exhibit similar gap magnitudes.

Distinct interband coupling behaviors are observed.

The superconductivity is nodeless and multigap in nature.

Abstract

A complex structure of the superconducting order parameter in $Ln_2$C$_3$ ($Ln$ = La, Y) is demonstrated by muon spin relaxation ($\mu$SR) measurements in their mixed state. The muon depolarization rate [$\sigma_{\rm v}(T)$] exhibits a characteristic temperature dependence that can be perfectly described by a phenomenological double-gap model for nodeless superconductivity. While the magnitude of two gaps is similar between La$_2$C$_3$ and Y$_2$C$_3$, a significant difference in the interband coupling between those two cases is clearly observed in the behavior of $\sigma_{\rm v}(T)$.