Gate-assisted phase fluctuations in all-metallic Josephson junctions

Abstract

We study the reduction of the supercurrent by a gate electrode in a purely metallic superconductor–normal metal–superconductor Josephson junction by performing, on the same device, a detailed investigation of the gate-dependent switching probability together with the local tunneling spectroscopy of the normal metal. We demonstrate that high energy electrons leaking from the gate trigger the reduction of the critical current which is accompanied by an important broadening of the switching histograms. The switching rates are well described by an activation formula including an additional term accounting for the injection of rare high energy electrons from the gate. The rate of electrons obtained from the fit remarkably coincides with the independently measured leakage current. Concomitantly, a negligible elevation of the local temperature in the junction is found by tunneling spectroscopy which excludes stationary heating induced by the leakage current as a possible explanation of the reduction of the critical current. This incompatibility is resolved by the fact that phase dynamics and thermalization effects occur at different timescales.