Sliding charge-density waves as a dynamic critical phenomenon

The dynamic properties of sliding charge-density waves are discussed in terms of a classical description of impurity pinning, with emphasis on the behavior near threshold considered as a dynamic critical phenomenon. A mean-field model introduced previously Phys. Rev. Lett. 50, 1486 (1983) is analyzed in detail, including ac response above and below threshold and hysteretic behavior below threshold. For short-range interactions, the weak-pinning limit is discussed and scaling behavior is predicted near threshold. The earlier prediction of ac noise with intensity inversely proportional to the square root of the volume with a diverging amplitude near threshold caused by a diverging correlation length is analyzed in terms of the scaling behavior; this interpretation of the noise is semiquantitatively confirmed by recent experiments of Mozurkewich and Gr\"uner Phys. Rev. Lett. 51, 2206 (1983). Many of the ideas presented here may be applicable to other systems, especially weakly pinned flux flow in type-II superconductors.