Collective dynamics of Josephson vortices in intrinsic Josephson junctions: exploration of in-phase locked superradiant vortex flow states

Abstract In order to explore the “superradiant” condition for the moving Josephson vortices in intrinsic Josephson junctions (IJJs), we perform large scale numerical simulations for the IJJs with realistic dimensions under a layer-parallel magnetic field (H>1T). Three clear step-like structures, at which we find structural transitions in moving flux-line lattice, are observed in the I–V curve. The flow states of the Josephson vortices are classified into four regions, from I to IV, according to the applied current or voltage values. The superradiant state, in which moving Josephson vortices forms the in-phase rectangular lattice, is stabilized in region III. In the superradiant state, the power spectra of excited electric fields show very sharp peak structures and the power at the peak position is very large. From the eigen mode analysis, we show that the step-like structure in the I–V curve corresponding to structural transitions in moving lattices originates from the resonances between the transverse Josephson plasma modes and the motion of the Josephson vortices.