Manifestation of quasiparticle branch imbalance in resistive measurements of mesoscopic superconductors

A model of the resistive state for mesoscopic superconductors has been proposed. It is considered that the frequency of thermally induced discrete phase-slip events is equal to the rate of thermally driven fluctuations, Gamma(T). After each phase slippage the nonequilibrium distribution of chemical potentials for pairs mu(p) and quasiparticles mu(q) relaxes on a time scale tau(Q)*. The measured time-averaged voltage across the mesoscopic sample with dimensions compared to a single phase-slip center is found to be proportional to the spatial difference of the corresponding chemical potential (mu(p) for superconducting probes and mu(q) for normal probes) and should be multiplied by the time averaging weight similar to tau(Q)*<Gamma(>)T. The resulting effective resistance ratio [R(T)]/R(normal) for mesoscopic objects may be noticeably greater than unity sufficiently close to the critical temperature; it displays a strong nonlinear dependence on the bias current and is greatly suppressed by an external magnetic field.