Low-temperature charge-density-wave dynamics and switching in NbSe3.

Abstract

We have studied charge-density-wave (CDW) transport in ${\mathrm{NbSe}}_{3}$ at temperatures below 45 K. Between the threshold electric field ${\mathit{E}}_{\mathit{T}}$ and a second characteristic field ${\mathit{E}}_{\mathit{T}}^{\mathrm{*}}$, the CDW conductivity varies as ${\mathrm{\ensuremath{\sigma}}}_{\mathrm{CDW}}$\ensuremath{\propto}exp(-\ensuremath{\Delta}/${\mathit{k}}_{\mathit{B}}$T), with an activation energy \ensuremath{\Delta} comparable to the CDW gap. Above ${\mathit{E}}_{\mathit{T}}^{\mathrm{*}}$, the CDW conductivity increases, in many crystals via an abrupt ``switch,'' to a much larger, only weakly temperature-dependent value. Contrary to previous suggestions, we find that ${\mathit{E}}_{\mathit{T}}^{\mathrm{*}}$ is determined by bulk CDW pinning and dynamics, not by isolated defects. We show that this behavior has strong analogs in the semiconducting CDW materials, and compare it with predictions based upon a model of CDW--normal-carrier interactions proposed by Littlewood.