Below T=40 K, charge-density wave (CDW) transport in NbSe3 is characterized by two
well-defined driving force thresholds ET and ET*.
Between these thresholds the CDW moves
extremely slowly with creep-like temperature and driving force dependencies. At the same
time, the CDW exhibits coherent oscillations with a frequency proportional to the CDW
current and having very narrow spectral widths, suggesting that the collective motion is
temporally ordered. We have extended our initial work to doped crystals containing
isoelectronic (Ta) and nonisoelectronic (Ti) impurities, and to crystals of different
thicknesses. These experiments show that the qualitative features are extremely robust, and
that the functional form of the creep velocity versus driving force and temperature is
consistent across all samples for currents ranging over five orders of magnitude. The
temperature dependence is consistent with processes having an energy comparable to the
CDW gap, but the field and impurity dependencies are inconsistent with all predicted
functional forms for creep in CDWs and related systems, and with our earlier picture of
amplitude collapse at each impurity. We compare our results to measurements of creep-like
behavior in other CDW and SDW systems, and discuss possible mechanisms.
Transverse Conductivity in the Sliding Charge-Density-Wave State ofNbSe3