MODE-LOCKING TRANSITIONS AND VORTEX FLOWS IN CURRENT-DRIVEN JOSEPHSON-JUNCTION ARRAYS

The dynamical behavior of overdamped de-driven Josephson-junction. arr ays is studied numerically in two dimensions. Currents varying linearl y along an edge are injected into the array and drawn out at the oppos ite edge either uniformly or through a busbar. The system is found to undergo a series of dynamical transitions as the gradient of the curre nt drive is increased. We show that, for ladder arrays, these transiti ons mark the loss of mode locking across specific bonds. The transitio ns cant alternatively, be associated with the onset of well-defined vo rtex flows. Spatial localization of vortices in individual plaquettes of a ladder, driven in the direction of its length, is seen to stabliz e quasiperiodicity of order N>3 in a certain region of the underlying parameter space. We also,discuss the extension of each of these featur es to full-fledged rectangular arrays.