Nonlocal electrodynamics of long ultranarrow Josephson junctions : Experiment and theory

Abstract We experimentally and theoretically investigate electromagnetic cavity modes in ultra-narrow Al-AlOx-Al and Nb-AlOx-Nb long Josephson junctions. Experiments show that the voltage spacing between the Fiske steps on the current-voltage characteristics of sub-μm wide and several hundred μm long Al-AlOx-Al and Nb-AlOx-Nb Josephson junctions increases when decreasing the width of a junction. This effect is explained by stray magnetic fields, which become important for narrow junctions. Theoretical estimates of the Fiske step voltage based on a nonlocal wave propagation equation are in good agreement with our experimental data. Using the nonlocal model, we determine the size and mass of a Josephson vortex by means of a variational approach, and relate vortex size to the experimentally measured critical magnetic field of the junction.