Frequency-dependent electric conductivity of field-induced spin-density waves in Bechgaard salts

We study theoretically the ac conductivity σ(ω,q) of field-induced spin-density waves (FISDW’s) in Bechgaard salts. We find that the electric current couples with the sliding motion of a FISDW. In the absence of SDW pinning the ac conductivity is the same as in the normal state if the quasiparticle damping is neglected. In the presence of the SDW pinning the low-frequency conductivity is much reduced from that in the normal state. However, when ω≫${\omega }_p$ the conductivity approaches that in the normal state, where ${\omega }_p$ is the pinning frequency. The sound velocity in a FISDW is also analyzed.