DYNAMIC CRITICAL PHENOMENA IN CHANNEL FLOW OF DRIVEN PARTICLES IN RANDOM-MEDIA

A simple model of the driven motion of interacting particles in a two- dimensional random medium is analyzed, focusing on the critical behavi or near to the threshold that separates a static phase from a flowing phase with a steady-state current. The critical behavior is found to b e surprisingly robust, being independent of whether the driving force is increased suddenly or adiabatically. Just above threshold. the flow is concentrated on a sparse network of channels, but the time scale f or convergence to this fixed network diverges with a larger exponent t han that for convergence of the current density to its steady-state va lue. This is argued to be caused by the ''dangerous irrelevance'' of d ynamic particle collisions at the critical point. Possible application s to vortex motion near to the critical current in dirty thin-film sup erconductors are discussed.