MODEL FOR THE FINE-STRUCTURE OF ZERO-FIELD STEPS IN LONG JOSEPHSON TUNNEL-JUNCTIONS AND ITS COMPARISON WITH EXPERIMENT

The single fluxon dynamics in the resonant regime has been investigate d on high-quality low-loss Nb/Al-ALO(x)/Nb window Josephson tunnel jun ctions. A new model accounting for the fine Structure of zero field st eps in linear junctions is proposed. Depending on the fluxon velocity and on the junction losses, resonances may occur between the fluxon an d the plasma waves corresponding to different wave numbers. This mecha nism relies on a single proposition that the fluxon experiences an acc eleration approaching the nonideal boundaries of the junction. We find good agreement between theory, numerical simulations, and experiments . The presence of the idle region has been proved to play a determinan t role for the occurrence of the fine structure. (C) 1996 American Ins titute of Physics.