Metastability and non-linear dynamics of sliding charge density waves.

Incommensurate charge-density-waves pinned by disorder show an interplay between spatial disorder and non-linear dynamics. At low electric fields close to and below the threshold field for sliding, their behavior is dominated by many degrees of freedom and low energy metastable states with a broad distribution of relaxation times. However the response to large a.c. driving fields shows features apparently characteristic of a system with relatively few degrees of freedom. The resolution of this paradox will be discussed.