DYNAMICAL EVIDENCE OF CRITICAL FIELDS IN JOSEPHSON-JUNCTIONS

We study the dynamical stability of phase configurations generated by an external magnetic field in long Josephson junctions. Depending on t he value of the field, the penetration of the vortex lines through the boundary of the junctions gives rise to different dynamical regimes w hose nature is characterized by measurements of Fiske singularities in the current-voltage characteristics of the junctions. The magnetic-fi eld dependence of the height of these singularities is compared with n umerical simulations of the sine-Gordon equation and low-temperature s canning electron microscopy of the junctions is performed in order to validate the dynamical patterns. For all the junctions that we have in vestigated, given their maximum pair current density j(c) and the Jose phson penetration depth lambda(j), we find that the external magnetic field that equals the critical value H-0 = 2 lambda(j)j(c), responsibl e for the trapping of a single static flux-quantum in the junction, pl ays a dominant role in establishing dynamical phase configurations. Bo th simulations and low-temperature scanning electron microscopy show c omplete analogy between the dynamical patterns of long and small-area junctions when H-0 is exceeded. [S0163-1829(97)02542-3].