Impurity scattering and frequency dependent conductivity in spin density waves

The quasiparticle contribution to the frequency dependent electric conductivity in the presence of randomly distributed impurities is calculated within mean field theory for spin density waves as formed in quasi one dimensional conductors like Bechgaard salts. Interchain hopping is taken into account and the effects of imperfect nesting are considered. In case of an electric field perpendicular to the chain direction there is no collective contribution to the conductivity and our results are directly applicable to recent measurements on both (TMTSF)2PF6 and quenched (TMTSF)2ClO4. The experimental data are well described by the theory in the clean limit, with somewhat larger scattering in the ClO4 salt.