NbReSi: A Noncentrosymetric Superconductor with Large Upper Critical\n Field

Abstract

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