DRIFT VELOCITY AND TEMPORAL PHASE FLUCTUATIONS OF SLIDING CHARGE-DENSITY WAVES IN RB0.3MOO3

The dynamics of CDW-s depinned by an electric field is investigated by transport, voltage noise and NMR measurments on a Rb0.3MoO3 single crystal. A direct measurement of the bulk winding rate νd of the sliding CDW phase is provided by the observation of sidebands in the motionally narrowed NMR spectra and by the oscillations of the spin echo amplitude as a function of the delay time. Comparison with the noise spectra confirms our earlier statement that νd is equal to the voltage noise frequency νn with an accuracy of 10%. Experimental NMR spectra at a field of E/ET ≈ 20 (E$-T$%/ is the depinning threshold) in the temperature range of 40 to 60 K have been fitted with high accuracy to lineshapes calculated under the assumption that the noise spectrum is related to the spatial current distribution in a simple way. Most of the experiments can be interpreted by considering the crystal as a collection of domains. In each domain the current is coherent for long times, we found in some cases a temporal coherence of 25-50 oscillation periods of the hyperfine field. We discuss stochastic variations of the CDW phase which become important at high temperatures, especially at fields near threshold.