Multiple frequency generation by bunched solitons in Josephson tunnel junctions

A detailed numerical study of a long Josephson tunnel junction modeled by a perturbed sine-Gordon equation demonstrates the existence of a variety of bunched soliton configurations. Thus, on the third zero-field step of the $V-I$ characteristic, two simultaneous adjacent frequencies are generated in a narrow bias current range. The analysis of the soliton modes provides an explanation of recent experimental observations.