Magnetic field dependence of relaxation times in nonequilibrium superconductors

We have investigated the effects of a magnetic field H on nonequilibrium quasiparticle relaxation processes in superconductoors by analyzing the I--V characteristics of long tin microbridges in a parallel field near T/sub c/(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 R/sub n/ of a nonequilibrium region of the bridge with length 2(Dtau/sub R/)/sup 1/2/, where D is the quasiparticle diffusion constant and tau/sub R/ is the transverse mode (branch imbalance) relaxation time. The magnitude and the temperature and field dependence of tau/sub R/ 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 Schoen. 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 I/sub c/, which isolates a single PSC and lowers the heat dissipation