Microwave conductivity of pinned spin-density waves and charge-density waves

We study the high-frequency conductivity of pinned spin- and charge-density waves within mean-field theory where the quasiparticle scattering is introduced explicitly in terms of randomly distributed nonmagnetic impurities. We find the ac response is approximated by the one for a damped harmonic oscillator, where the damping constant is expressed in terms of microscopic parameters. In particular, the phason damping constant in a charge-density wave is reduced by m/$m^{\mathrm{*}}$ compared with the one in a spin-density wave, where $m^{\mathrm{*}}$ is the phason mass and m is the band electron mass.