Super-relativistic fluxon in a Josephson multilayer : Experiment and simulation

The propagation of a single Josephson vortex is studied experimentally in stacks of five and ten $Nb-Al/AlOₓ-Nb$ annular Josephson tunnel junctions. To gain a detailed insight in the dynamics of the system, experimental data are compared to numerical simulations. This comparison enables us to determine the particular junction in the stack in which the vortex is located. We study in detail the interaction of the vortex with the Josephson plasma oscillations at different temperatures that correspond to different dissipation values. At low temperatures, the resonant locking of the vortex to the emitted Cherenkov waves is observed. At high temperatures, the nonresonant behavior of the vortex is found. Experimental data, simulation, and analytical models are in good agreement, and show a consistent picture of the dynamics of a single vortex in the stack.