BUNCHED FLUXON STATES IN ONE-DIMENSIONAL JOSEPHSON-JUNCTION ARRAYS

Dynamics of fluxons in a discrete Josephson transmission line is inves tigated, combining numerical simulations and an analytical approach. I t is found that, in different ranges of the parameters (the driving de bias current and dissipative constant), two fluxons (2 pi-kinks) may form either a bifluxon (4 pi-kink), or various bound states (2 pi+2 pi -kinks with a finite separation), which can stably propagate along the Line. The stability of these states is investigated as a function of the kink velocity. An analytical approach is based on prediction of fo rmation of a two-kink bound state through the interaction mediated by their oscillating ''tails.'' At small velocities, a satisfactory agree ment is found between the analysis and the numerical results. At still smaller velocities, a new phenomenon is predicted analytically and fo und numerically, viz., transition from an asymmetric ''tailed'' kink t o a symmetric tailless one. Conditions for experimental observation of the predicted behavior, as well as its practical consequences for the fluxon propagation in the discrete Josephson transmission lines, are discussed too.