Impulse response of the switching charge-density-wave conductor NbSe₃

When a switching charge-density-wave (CDW) conductor is driven with a rectangular voltage pulse, the CDW begins to slide only after a delay τ. We present detailed measurements of the impulse response of the charge-density-wave conductor NbSe₃ as a function of the pulse height, temperature, and initial configuration. We find that the average conduction delay τ¯ has an activated temperature dependence for pulse heights sufficiently far above threshold: τ¯∝exp(E_a/k_BT), where E_a=24.1±3.2 meV, comparable to the CDW gap. We have also performed numerical experiments based on a model which includes the interaction of the CDW with uncondensed electrons. Within this model, we can account for the polarization dependence of the threshold for sliding and the dependence of the conduction delay on the pulse height. If we assume that the ungapped carriers in NbSe₃ do not screen the motion of the CDW, then the Arrhenius temperature dependence of the delayed conduction can also be explained. The excellent qualitative agreement between theory and experiment provides a compelling argument that switching behavior arises from the interaction of the CDW with uncondensed carriers.