Decoupling of ac dynamics from dc polarization below threshold for charge-density waves in NbSe3

Experiments on nonlinear charge-density wave motion in Nb${\mathrm{Se}}_3$ demonstrate that the small-signal ac dynamics for megahertz frequencies is effectively decoupled from the dc response for bias voltages $\left|V_0\right|<\mathrm{}{V}_T$ below threshold. Mixing signals generated at megahertz frequencies indicate an effective dc voltage $V_0^{\prime }=0\mathrm{}$ for all $\left|V_0\right|<\mathrm{}{V}_T$ in this region. This ac-dc decoupling is further illustrated by rectification measurements made in the presence of a large-amplitude ac signal. The results are consistent with a revised tunneling theory, but inconcistent with the simplest classical model.