Study of Nb0.18Re0.82 non-centrosymmetric superconductor in the normal and superconducting states

Abstract

We examine the evidence for multiband superconductivity and non s-wave pairing in the non-centrosymmetric superconductor (NCS) Nb0.18Re0.82, using electrical transport, magnetization and specific heat measurements. In the normal state, the evolution of electrical resistivity with temperature and magnetic field support the phonon-assisted interband scattering and multiband picture. In the superconducting state, the temperature dependence of the upper critical field, , is found linear and cannot be described within the Werthamer, Helfand and Hohenberg model over the whole temperature range measured. In addition, the observed exceeds the Pauli limit, suggesting non-s-wave pairing. Interestingly, the Kadowaki–Woods ratio and Uemura plot reveal a behavior in Nb0.18Re0.82 which is similar to that found in unconventional superconductors. The normalized superfluid density (ρs), estimated using the temperature dependence of the lower critical field, , is well explained with the help of the multiband description. Phase fluctuation analysis conducted on the reversible magnetization data, reveals a significant deviation from the mean-field conventional s-wave behavior. This trend is interpreted in terms of a non s-wave spin-triplet component in the pairing symmetry as might be anticipated in a NCS where anti-symmetric spin–orbit coupling plays a dominant role. Recently, time reversal symmetry breaking observed in Nb0.18Re0.82 supports this picture.