Cherenkov radiation in coupled long Josephson junctions

Evidence for Cherenkov radiation of a Josephson vortex is observed in the system of two magnetically coupled long Josephson junctions. This radiation leads to resonances which appear above the lowest characteristic velocity $c_{-}$ of the linear electromagnetic waves. Resonances result from interaction of a Cherenkov wave with a moving Josephson vortex and, in annular junctions, occur when the vortex makes one turn around the junction. Experimental data are in good agreement with the proposed model and simulations which provide a clear physical picture of the observed effect.