Fluxon density waves in long Josephson junctions

Numerical simulations of the multiple fluxon dynamics stimulated by an external oscillating force applied at a boundary of a long Josephson junction are presented. The calculated IV characteristics agree well with a recent experimental observation of rf-induced satellite flux-flow steps. The voltage spacing between the satellites and the main flux-flow step corresponds to the second harmonic of the external frequency. We find that the satellite flux-flow modes are characterized by collective excitations propagating through the fluxon chain. These dynamical states can be interpreted as fluxon density waves.