Superconductivity in Rh$_2$Ga$_9$ and Ir$_2$Ga$_9$ without Inversion Symmetry

TL;DR

This study reports the discovery of superconductivity around 2 K in Rh$_2$Ga$_9$ and Ir$_2$Ga$_9$, the first in these binary systems, with both exhibiting weak-coupling BCS behavior and lacking inversion symmetry.

Contribution

First observation of superconductivity in Rh-Ga and Ir-Ga binary systems, revealing weak-coupling BCS superconductivity in non-centrosymmetric structures.

Findings

Rh$_2$Ga$_9$ and Ir$_2$Ga$_9$ superconduct at ~2 K

Rh$_2$Ga$_9$ is type-I, Ir$_2$Ga$_9$ is type-II

Both are weak-coupling BCS superconductors

Abstract

Superconductivity with $T_{\rm c}$ $\simeq$ 2 K was discovered in the intermetallic binary compounds Rh$_2$Ga$_9$ and Ir$_2$Ga$_9$. This is the first observation of superconductivity in the Rh-Ga and Ir-Ga binary systems. Both compounds crystallize in a distorted Co$_2$Al$_9$-type structure (monoclinic, space group: $Pc$), which lacks spatial inversion symmetry. Specific heat measurements revealed that both compounds are weak-coupling BCS superconductors having an isotropic superconducting gap. Measurements in magnetic fields indicated type-I superconductivity with a critical field $H_{\rm c}(0)$ $\simeq$ 130 Oe for Rh$_2$Ga$_9$ and type-II superconductivity with an upper critical field $H_{\rm c2}(0)$ $\simeq$ 250 Oe for Ir$_2$Ga$_9$.