Anomalously large Josephson switching currents in low dissipation Josephson junctions

The authors observed marked effects on the switching characteristics of a high-quality junction due to the frequency dependence of the external circuitry. This involved anomalously high values of the maximum switching current of Josephson junctions at temperatures where thermally activated switching was expected to greatly lower it. This effect was modeled by evaluating junction parameters from the measured characteristics. The junction resistance determined from the return switching current is that of a nearly ideal quasiparticle tunneling resistance, increasing exponentially fast at low temperatures. As a result, the load resistance becomes dominant over a wide range of temperatures. The frequency dependence of this load resistance then produces the anomalously large Josephson switching currents, which have not been observed previously in junctions with significant normal conductance.>