NOVEL AXISYMMETRICAL COHERENT VORTEX STATE IN ARRAYS OF JOSEPHSON-JUNCTIONS FAR FROM EQUILIBRIUM

We present a numerical study of a topologically disordered, overdamped, array of Josephson junctions subjected to dc and ac currents. We find that vortices are nucleated by the ac current, apart from the ones produced at defects. After a complex transient, these vortices settle into a parity-broken time-periodic, axisymmetric coherent vortex state characterized by rows of vortices lying along a tilted axis. This locked-in state leads to giant half-integer pseudosteps in the I-V characteristics that are hysteretic in nature. Possible connections of these results to recent experiments are discussed.