Effect of electric fields on the propagation of ultrasonic pulses ino-TaS3

We report results on the velocity and attenuation of 10-MHz ultrasonic pulses in o-${\mathrm{TaS}}_3$ in the charge-density-wave state and in the presence of electric fields. For applied voltages greater than the threshold voltage for nonlinear conductivity the elasticity was found to decrease and sound absorption to increase. The changes in elasticity are orders of magnitude smaller than those reported for kHz frequencies. A relaxation mechanism for sound absorption is proposed with a relaxation strength and a relaxation time that are functions of temperature as well as of applied voltage. The model further suggests that results of elastic measurements could be strongly sample dependent. A search for a shift in sound velocity as a result of a drifting charge-density wave found an effect an order of magnitude larger than predicted shifts. Possible reasons are discussed.