Relaxation and elastic anomalies in charge-density-wave conductors

We have measured electric-field-dependent anomalies in the dynamic Youngs and shear moduli and internal friction of the charge-density-wave (CDW) conductors TaS3 and NbSe3 at different mechanical frequencies and field (i.e., current) frequencies f. For TaS3 in a dc field, the anomalies decrease with increasing, for /2>300 Hz; this decrease is independent of the amplitude of the resonance, indicating that we are remaining in a conventional elastic limit. For 13</2<300 Hz, the anomalies are independent of, implying that below the CDW depinning threshold, the average relaxation time >10 ms. Reversal of the field at frequency f introduces an internal friction peak at f=/2 and a decrease in the internal friction at high f for both materials. These and previous results are discussed in terms of relaxational models.