Measurement of the spatial distribution of the maximum Josephson current in superconducting tunnel junctions

The spatial distribution of the maximum Josephson current density J_max is imaged in quasi-one-dimensional in-line tunnel junctions by scanning the junction surface with an electron beam and by recording the beam-induced change of I_max as a function of the coordinates of the beam focus. In addition to the modulation of the Josephson current density for the different vortex states, the nonlocal effect resulting from the beam-induced change of the phase-difference function is observed. The results are in good agreement with the theoretical predictions. The electron beam scanning technique also serves well for imaging inhomogeneities in the barrier or in the electrodes of the junction.