MAGNETIC-FIELD DEPENDENCE OF RELAXATION-TIMES IN NON-EQUILIBRIUM SUPERCONDUCTORS

We have investigated the effects of a magnetic field H on nonequilibrium quasiparticle relaxation processes in superconductors by analyzing the I-V characteristics of long tin microbridges in a parallel field near Tc(H). Following Skocpol, Beasley, and Tinkham, we take the differential resistance of a given phase-slip center (PSC) to be approximately equal to the normal resistance Rn of a nonequilibrium region of the bridge with length 2(DΤR)1/2, where D is the quasiparticle diffusion constant andΤR is the transverse mode (branch imbalance) relaxation time. The magnitude and the temperature and field dependence ofΤR as inferred from our data agree well with those of the transverse mode relaxation time in the presence of pair-breaking, derived by Schmid and Schön. The longitudinal mode disequilibrium is interpreted in terms of local heating proportional to IV, and the resulting distortions in the I-V characteristics are corrected. Most of our samples contain a deliberate weak spot with a depressed critical current Ic, which isolates a single PSC and lowers the heat dissipation(~Ic2Rn). © 1978 Plenum Publishing Corporation.