Soliton Dynamics and Zero Field Steps in Josephson Tunnel Junctions

The zero field steps in the current-voltage characteristic of Josephson tunnel junctions are explained as a manifestation of the oscillatory motion of N solitons in the tunnelling barrier. Here N is the step number. The solitons evolve according to a perturbed sine-Gordon equation and numerical solutions of this equation explain the zero field steps as well as many features of the emitted microwave radiation.