Direct probing of the spatial distribution of the maximum Josephson current in a superconducting tunnel junction

We report the first experimental results obtained by low-temperature scanning-electron microscopy on the spatial distribution of the maximum Josephson current in tunnel junctions. The experiments were performed with a nearly one-dimensional PbIn-PbBi window junction, its length being large compared to J. The spatial resolution is 1-2 m and is governed by the thermal healing length. In a parallel magnetic field the different vortex states have been clearly observed. The nonlocal effects due to the beam-induced change of the phase-difference function predicted by Chang et al. have also been confirmed.