Vortex radiation in long narrow Josephson junctions: Theory and experiment

摘要

We study theoretically and experimentally the dynamics of vortices in long, extremely narrow Josephson junctions. Using a variational approach, the current-voltage characteristics are calculated for junctions of different widths. The analytically and numerically calculated current-voltage characteristics show good agreement. We find that the decrease of the junction width leads to a substantial increase of the maximum velocity of vortices. Due to the interaction with stray magnetic fields outside the junction, the vortices radiate Cheren-kov waves as they move in the junction. Locking of the vortex oscillation frequency to that of the Cherenkov radiation leads to novel resonances on the current-voltage characteristics. We observe such resonances in experiments, and their voltage positions and current magnitudes are in qualitative agreement with our theoretical analysis.