Sliding charge-density waves as rough growth fronts

Using high-resolution x-ray scattering techniques, we have measured the tra nsverse static structure factor of the sliding charge-density wave (CDW) in NbSe3. For temperatures between 70 and 120 K and for applied currents up t o 40 times the threshold current for sliding, the scattering peak for the s liding CDW is significantly broader than that for the pinned CDW, indicatin g that the sliding state is less correlated than the pinned state. Using sc aling analysis, we show that the CDW phase roughness exponent ct rises from 0.60 +/- 0.01 in the pinned state to 0.80 +/- 0.01 in the sliding state, i ndicating that the phase fronts of the sliding CDW are significantly roughe r than those of the pinned CDW.