Interactions of Sliding Charge-Density Waves with Phonons

While it is well known that the depinning of a charge-density wave (CDW) in a quasi-onedimensional conductor causes unusual electron transport properties, it also affects the lattice phonons in surprising ways. In this paper, we discuss two such effects. In orthorhombic TaS3, depinning causes low-frequency acoustic velocities to decrease, presumably because the local phase of the CDW can relax in an oscillating strain when it is depinned. We have used torsional oscillator measurements to determine the voltage dependence of the average relaxation time. In monoclinic K0.3MoO3, we have measured changes in the frequencies, oscillator strengths, and bandwidths of optic phonons near current contacts. The sign of these changes depends on the polarity of the current, indicating that they are due to polarization of the CDW which accompanies depinning