NbReSi: A Noncentrosymetric Superconductor with Large Upper Critical Field

TL;DR

This paper reports the discovery of superconductivity in noncentrosymmetric NbReSi with a high upper critical field, fully gapped superconducting state, and potential for exploring time-reversal symmetry breaking in Re-based superconductors.

Contribution

It introduces NbReSi as a new noncentrosymmetric superconductor with notable properties, including a large upper critical field and insights into its electronic structure.

Findings

Superconducting transition temperature T_c = 6.5 K

Large upper critical field μ_0H_c2(0) ≈ 12.6 T

Electronic structure dominated by Re and Nb d-orbitals

Abstract

We report the discovery of superconductivity in noncentrosymmetric NbReSi, which crystallizes in a hexagonal ZrNiAl-type crystal structure with space group $P\bar{6}2m$ (No.~189). Bulk superconductivity, with $T_c$ = 6.5 K was characterized via electrical-resistivity, magnetization, and heat-capacity measurements. The low-temperature electronic specific heat suggests a fully gapped superconducting state in NbReSi, while a large upper critical field of $\mu_0H_\mathrm{c2}(0)$ $\sim$ 12.6 T is obtained, which is comparable to the weak-coupling Pauli limit. The electronic band-structure calculations show that the density of states at the Fermi level are dominated by Re and Nb $d$-orbitals, with a sizeable band splitting induced by the antisymmetric spin-orbit coupling. NbReSi represents another candidate material for revealing the puzzle of time-reversal symmetry breaking observed in some Re-based superconductors and its relation to the lack of inversion symmetry.