We systematically investigate the normal and superconducting properties of noncentrosymmetric ${\mathrm{Re}}_6\mathrm{Zr}$ using magnetization, heat capacity, and electrical resistivity measurements. Resistivity measurements indicate ${\mathrm{Re}}_6\mathrm{Zr}$ has poor metallic behavior and is dominated by disorder. ${\mathrm{Re}}_6\mathrm{Zr}$ undergoes a superconducting transition at $T_{\mathrm{c}}=\left(6.75\pm 0.05\right)$ K. Magnetization measurements give a lower critical field, ${\mu }_0{H}_{\mathrm{c}1}=\left(10.3\pm 0.1\right)$ mT. The Werthamer-Helfand-Hohenberg model is used to approximate the upper critical field ${\mu }_0{H}_{\mathrm{c}2}=\left(11.2\pm 0.2\right)\mathrm{T}$, 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 ${\mathrm{Re}}_6\mathrm{Zr}$ 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.

• Received 12 May 2017
• Corrected 7 September 2017

DOI:https://doi.org/10.1103/PhysRevB.96.064521