Physical properties of the noncentrosymmetric superconductor Nb0.18Re0.82

Abstract

We report the synthesis and measurements of magnetic, transport, and thermal properties of polycrystalline ${\mathrm{Nb}}_{0.18}{\mathrm{Re}}_{0.82}$, which has a superconducting transition at ${T}_{c}$ \ensuremath{\sim} 8.8 K. The noncentrosymmetric \ensuremath{\alpha}-Mn structure of the compound is confirmed by x-ray diffraction. Using the measured values for the lower critical field ${H}_{c1}$, upper critical field ${H}_{c2}$, and the specific heat $C$, we estimate the thermodynamic critical field ${H}_{c}$(0), coherence length \ensuremath{\xi}(0), penetration depth \ensuremath{\lambda}(0), and the Ginzburg-Landau parameter \ensuremath{\kappa}(0). The specific heat jump at ${T}_{c}$, \ensuremath{\Delta}C/$\ensuremath{\gamma}{T}_{c}$ $=$ 1.86, suggests that ${\mathrm{Nb}}_{0.18}{\mathrm{Re}}_{0.82}$ is a moderately coupled superconductor. Below ${T}_{c}$ the electronic specific heat decays exponentially, suggesting that the gap is isotropic. Our data suggest that the triplet admixture is weak in the polycrystalline form of compound. However, the estimated value of the upper critical field ${H}_{c2}$(0) is close to the calculated Pauli limit.