Limiting response times in a granular niobium weak link

We have measured rf SQUID characteristics of a granular niobium weak link as a function of frequency from 20 MHz to 9 GHz. A degredation in the SQUID performance and a critical current enhancement is correlated with the a non-equilibrium site decay time as inferred from the frequency dependence of the critical current hysteresis. At low frequencies, the electromagnetic response time extracted from the frequency dependent SQUID modulation is found to be of the same order of magnitude as the quasiparticle inelastic scattering time. The electromagnetic response time is found to decrease at temperatures and frequencies where the critical currents are enhanced. The large (an order of magnitude) critical current enhancement seems to be associated with the granular nature of the weak link.