Harmonic generation and scaling behavior in sliding-charge-density-wave conductors

The generation of harmonics of a small ac modulation field is used, in conjunction with the standard current-voltage measurement, to study the depinning behavior in well-characterized and high-purity samples of the charge-density-wave conductor ${\mathrm{NbSe}}_3$. The results show that the current carried by the charge density wave obeys a scaling law: $I_{\mathrm{CDW}=\left[\right(\mathrm{V}\mathrm{-}{V}_T)/V_T{]}^{\zeta }}$ with ζ=1.23±0.07. Implications of this result on the various theoretical models of the dynamics of the sliding state are discussed.