DYNAMICAL FRICTION AND INSTABILITY OF INTERFACE MOTION

An elastic body moving in a quenched random force environment with a s ingular force correlator experiences an additional friction force whic h is inversely proportional to velocity. This dynamical friction mecha nism is important, e.g., for a moving interface which is subjected to quenched random pinning forces. For sufficiently strong pinning forces , interface motion becomes unstable at values of driving force smaller than some critical one and the interface velocity drops. We expect in this case a first-order depinning transition with hysteresis in the d ependence of the interface velocity on driving force. Instability in t he interface motion remains under perturbations like an additional per iodic driving force or thermal fluctuations. Interface motion instabil ity can also take place in systems with small viscosity, when inertial effects are important.