The dielectric response of sliding charge density waves.

The linear response of a model of deformable charge density waves pinned by weak disorder is calculated, including the screening effects of free carriers. Owing to the screening of localized pinned collective oscillations, the dielectric function develops a low frequency loss peak in addition to the expected absorption close to the pinning frequency. These results provide a quantitative explanation of the apparent discrepancies between low frequency (~10MHz) electrical measurements and higher frequency (microwave or infrared) measurements of the dielectric response.