X-RAY-SCATTERING MEASUREMENTS OF THE TRANSIENT STRUCTURE OF A DRIVEN CHARGE-DENSITY-WAVE

We report time-resolved x-ray-scattering measurements of the transient structural response of the sliding Q(1) charge-density wave (CDW) in NbSe3 to a reversal of the driving electric field. The observed time s cale characterizing this response at 70 K varies from similar to 15 ms ec for driving fields near threshold to similar to 2 msec for fields w ell above threshold. The position and time-dependent strain of the CDW is analyzed in terms of a phenomenological equation of motion for the phase of the CDW order parameter. The value of the damping constant, gamma = (3.2 +/- 0.7) x 10(-19) eV sec Angstrom(-3), is in excellent a greement with the value determined from transport measurements. As the driving field approaches threshold from above, the line shape becomes bimodal, suggesting that the CDW does not depin throughout the entire sample at one well-defined voltage.