SOLITON DYNAMICS IN 2-DIMENSIONAL JOSEPHSON TUNNEL-JUNCTIONS

We observed a zero-field current step (ZFS) in several square Josephso n tunnel junctions of intermediate size (i.e., size congruent-to lambd a(j)). This step clearly shows soliton-type motion along the two diago nals of the junction as predicted by Turlot et al. [Phys. Rev. B 42, 8 418 (1990)), called isoperimetric pattern dynamics (IPD). In addition to the information given by the current-voltage characteristic, the dy namical behavior is investigated using low temperature scanning electr on microscopy (LTSEM). In parallel, extensive numerical simulations ar e performed to simulate the effect of the LTSEM ''hot spot'' on the IP D dynamics governed by a two dimensional perturbed sine-Gordon equatio n. The comparison between the experimental data obtained by the LTSEM technique and numerical simulations clearly shows the validity of the IPD model in order to explain the observed ZFS.