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 investigated on high-quality low-loss Nb/Al-ALO(x)/Nb window Josephson tunnel junctions. A new model accounting for the fine Structure of zero field steps in linear junctions is proposed. Depending on the fluxon velocity and on the junction losses, resonances may occur between the fluxon and the plasma waves corresponding to different wave numbers. This mechanism relies on a single proposition that the fluxon experiences an acceleration 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 determinant role for the occurrence of the fine structure. (C) 1996 American Institute of Physics.