Dynamic transition in vortex flow in strongly disordered Josephson junction arrays and superconducting thin films

We study the dynamics of vortices in strongly disordered $d=2$ Josephson junction arrays and superconducting films driven by a current. We find a dynamic phase transition in vortex flow at a current $I_p>I_c$. Below $I_p$ there is plastic flow characterized by an average-velocity correlation length scale $\xi_v$ in the direction of motion, which diverges when approaching $I_p$. Above $I_p$ we find a moving vortex phase with homogeneous flow and short range smectic order. A finite size analysis shows that this phase becomes asymptotically a liquid for large length scales.