Superconducting and normal-state properties of the noncentrosymmetric superconductor Re6Zr

TL;DR

This study characterizes the superconducting and normal-state properties of Re6Zr, revealing its fully gapped s-wave superconductivity, disorder effects, and unconventional vortex behavior, contributing to understanding non-centrosymmetric superconductors.

Contribution

It provides a comprehensive experimental analysis of Re6Zr's superconducting properties, including critical fields, gap symmetry, and vortex dynamics, highlighting its unconventional features.

Findings

Re6Zr has a superconducting transition at 6.75 K.

Re6Zr exhibits a fully gapped s-wave superconducting state.

Unusual flux pinning indicates an unconventional vortex state.

Abstract

We systematically investigate the normal and superconducting properties of non-centrosymmetric Re$_{6}$Zr using magnetization, heat capacity, and electrical resistivity measurements. Resistivity measurements indicate Re$_{6}$Zr has poor metallic behavior and is dominated by disorder. Re$_6$Zr undergoes a superconducting transition at $T_{\mathrm{c}} = \left(6.75\pm0.05\right)$ K. Magnetization measurements give a lower critical field, $\mu_{0}H_{\mathrm{c1}} = \left(10.3 \pm 0.1\right)$ mT. The Werthamer-Helfand-Hohenberg model is used to approximate the upper critical field $\mu_{0}H_{\mathrm{c2}} = \left(11.2 \pm 0.2\right)$ T which is close to the Pauli limiting field of 12.35 T and which could indicate singlet-triplet mixing. However, low-temperature specific-heat data suggest that Re$_{6}$Zr is an isotropic, fully gapped s-wave superconductor with enhanced electron-phonon coupling. Unusual flux pinning resulting in a peak effect is observed in the magnetization data, indicating an unconventional vortex state.