Vortex dynamics in disordered Josephson junction arrays: from plastic   flow to flux flow
  We study the dynamics of Josephson junction arrays with positional disorder and driven by an external current. We consider weak magnetic fields, corresponding to a frustration $f=n+1/25$ with $n$ integer. We find that above the critical current $i_c$ there is a plastic flow of vortices, where most of the vortices are pinned and only a few vortices flow through channels. This dynamical regime is characterized by strong fluctuations of the total vorticity. The number of the flow channels grow with increasing bias current. At larger currents there is a dynamical regime characterized by the homogeneous motion of all the vortices, i.e. a flux flow regime. We find a dynamical phase transition between the plastic flow and the flux flow regimes when analyzing voltage-voltage correlation functions. 
Daniel Dominguez (Centro Atomico Bariloche, Argentina)