DIMENSIONALITY DEPENDENCE OF MODE-LOCKING DYNAMICS IN CHARGE-DENSITY-WAVE TRANSPORT

We estimate the widths of the harmonic mode-locked steps observed on t he de I-V characteristic of charge-density-wave (CDW) conductors when ac and dc voltages are applied together using the classical deformable medium model. For weakly pinned CDW's in the high-velocity limit, del taE(p)/1/E(T) = 2\J(p)(omega(c)0E(ac)/omega(ac)E(T))\4/(4-D) where del taE(p/1) is the width in electric field of the p/1 step and D is the e ffective dimension of the pinning. An analytic argument suggests that the phase deformations are much larger in the mode-locked state than i n the normal sliding state. They are largest for ac amplitudes that yi eld maxima in the step width. On the p/1 step the time-averaged phase- phase correlation length is predicted to vary as deltaE(p/1)-1/2. Thes e analytic estimates are supported by numerical simulations. Measureme nts of the step width variation with ac amplitude and frequency for Nb Se3 crystals whose static pinning is two dimensional (2D) are consiste nt with the 2D step width prediction.