Dynamics of charge-density waves in the presence of free carriers

The response of an unpinned, incommensurate charge-density wave (CDW) to external perturbations in the presence of free quasiparticles is studied. The CDW can act as a charged lattice but the proportion of the total charge density assigned to the CDW and to quasiparticles depends on the external conditions. If the collisions between quasiparticles can be ignored, the effective charge of the CDW is different in the static and dynamic limits. In the static limit the quasiparticles relax to screen spatial variations and the form is analogous to that used for superfluids. In the dynamic limit the quasiparticles do not renormalize the effective charge. In the presence of collisions the effective charge depends on the distribution of quasiparticles which in turn depends on the relative importance of various scattering rates. In general, a simple two-fluid model is not applicable.