Low frequency charge dynamics of incommensurate chromium alloys

Chromium alloys order as spin-density-wave (SDW) state antiferromagnets below the Néel temperature T_N. The formation of a SDW with wavevector Q_±^′ is accompanied by the simultaneous formation of a charge-density-wave (CDW) with wavevector 2Q_±^′. We present the first results for the dynamics of the CDW within the random phase approximation. Phason modes arising from the translational invariance of the free energy are the only Goldstone modes involved in the charge dynamics of chromium alloys. The charge phasons have a nearly linear dispersion at low frequencies with a velocity which approaches the spin-wave velocity as T→T_N. We obtain the neutron and x-ray scattering strengths and comment on the observability of the charge phasons.