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

We examine the evidence for multiband superconductivity and non s-wave pairing in the non-centrosymmetric superconductor Nb0.18Re0.82, using electrical transport, magnetization and spe-cific heat measurements. In the normal state, the evolution of electrical resistivity with temperatureand magnetic field support the phonon assisted interband scattering and multiband picture. Inthe superconducting state, the temperature dependence of the upper critical field,Hc2(T), is foundlinear and can not be described within the Werthamer, Helfand and Hohenberg (WHH) model overthe whole temperature range measured. In addition, the observedHc2(0) exceeds the Pauli limit,suggesting non-s-wave pairing. Interestingly, the Kadowaki-Woods ratio and Uemura plot reveala behavior in Nb0.18Re0.82which is similar to that found in unconventional superconductors. Thenormalized superfluid density (ρs), estimated using the temperature dependence of the lower criticalfield,Hc1(T), is well explained with the help of the multiband description. Phase-fluctuation analysisconducted on the reversible magnetization data, reveals a significant deviation from the mean-fieldconventional s-wave behavior. This trend is interpreted in terms of a non s-wave spin-triplet com-ponent in the pairing symmetry as might be anticipated in a non-centrosymmetric superconductorwhere anti-symmetric spin-orbit coupling plays a dominant role. Recently, time reversal symmetrybreaking (TRSB) observed in Nb0.18Re0.82supports this picture