Viscoelastic depinning of driven systems: Mean-field plastic scallops

We have investigated the mean-field dynamics of an overdamped viscoelastic medium driven through quenched disorder. The model allows for the coexisten ce of pinned and sliding regions and can exhibit continuous elastic depinni ng or first-order hysteretic depinning. Numerical simulations indicate mean -field instabilities that correspond to macroscopic stick-slip events and l ead to premature switching. The model describes the elastic and plastic dyn amics of driven vortex arrays in superconductors and other extended disorde red systems.