Relaxation and elastic anomalies in charge-density-wave conductors

We have measured electric-field-dependent anomalies in the dynamic Young’s and shear moduli and internal friction of the charge-density-wave (CDW) conductors ${\mathrm{TaS}}_3$ and ${\mathrm{NbSe}}_3$ at different mechanical frequencies ω and field (i.e., current) frequencies f. For ${\mathrm{TaS}}_3$ in a dc field, the anomalies decrease with increasing ω, for ω/2π>300 Hz; this decrease is independent of the amplitude of the resonance, indicating that we are remaining in a conventional elastic limit. For 13<ω/2π10 ms. Reversal of the field at frequency f introduces an internal friction peak at f=ω/2π and a decrease in the internal friction at high f for both materials. These and previous results are discussed in terms of relaxational models.