Discovery of the Type-II Superconductor Ta$_4$Rh$_2$C$_{1-\delta}$ with a High Upper Critical Field

TL;DR

This paper reports the discovery of a new type-II superconductor, Ta$_4$Rh$_2$C$_{1-\delta}$, with a high upper critical field exceeding the Pauli limit, expanding the understanding of superconducting materials.

Contribution

The paper introduces a previously unknown superconductor with a high upper critical field surpassing the Pauli limit, and characterizes its structural and superconducting properties.

Findings

Superconductor Ta$_4$Rh$_2$C$_{1-\delta}$ has $T_c$ = 6.4 K.

It exhibits a high upper critical field of 17.4 T.

The compound exceeds the BCS Pauli limit for critical field.

Abstract

We report on the discovery of superconductivity in the previously unknown compound Ta$_4$Rh$_2$C$_{1-\delta}$. Ta$_4$Rh$_2$C$_{1-\delta}$ crystallizes in the $\eta$-carbide structure type, in the cubic space group $Fd\bar{3}m$ (No.227) with a unit cell parameter of $a = $ 11.7947 \AA. Temperature-dependent magnetic susceptibility, resistivity, and specific heat capacity measurements reveal that Ta$_4$Rh$_2$C$_{1-\delta}$ is a type-II bulk superconductor with a critical temperature of $T_{\rm c}$ = 6.4 K, and a normalized specific heat jump $\Delta C/\gamma T_{\rm c}$ = 1.56. Notably, we find Ta$_4$Rh$_2$C$_{1-\delta}$ has a high upper critical field of $\mu_0 H_{\rm c2}{\rm (0)}$ = 17.4 T, which is exceeding the BCS weak coupling Pauli limit of $\mu_0 H_{\rm Pauli}$ = 11.9 T.