Non‐linear conductivity of charge‐density‐wave systems

We consider the problem of sliding motion of a charge‐density‐wave subject to static disorder within an elastic medium model. Starting with a field‐theoretical formulation, which allows exact disorder averaging, we propose a self‐consistent approximation scheme to obtain results beyond the standard large‐velocity expansion. Explicit calculations are carried out in three spatial dimensions. For the conductivity, we find a strong‐coupling regime at electrical fields just above the pinning threshold. Phase and velocity correlation functions scale differently from the high‐field regime, and static phase correlations converge to the pinned‐phase behaviour. The sliding charge‐density‐wave is accompanied by narrow‐band noise.