Glassy Motion of Elastic Manifolds.

We discuss the low-temperature dynamics of an elastic manifold driven through a random medium. For driving forces well below the {ital T}=0 depinning force, the medium advances via thermally activated hops over the energy barriers separating favorable metastable states. We show that the distribution of waiting times for these hopping processes scales as a power law. This power-law distribution naturally yields a nonlinear glassy response for the driven medium, {ital v}{approximately}exp({minus}const{times}{ital F}{sup {minus}{mu}}). {copyright} {ital 1996 The American Physical Society.}