Transport Properties of Charge-Density Waves

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Abstract
The remarkable electrical behaviour of NbSe3 and a few other quasi low-dimensional metals arises from the presence, at low enough temperatures, of charge-density waves (CDWs) which can be set into motion by an applied electric field. This entails a co-opearative motion of the electrons, essentially as suggested by Frohlich (1954), and leads to non-linearity, non-locality and freqancy-dependence in the conduction, the appearance of periodic components of current in a steady field, syncronization phenomena when alternating and direct fields are applied together, and a veriety of hysteresis and memory effects. Explanations of this behaviour have mostly been based on semi-classical phenomenological models, in which the CDW is regarded as an elastically deformalble object, pinned to the lattice by randomly distributed impurities. However, the experimental evidence leaves some doubt as to whether the important physical processes have been correctly identified, and progress at a microscopic level has been rather limited. In this survey of charge-density wave transport, the extent to which recent experimental work makes it necessary to abandon the conventional picture of the moving CDW "sliding" over impurities is considered. It is concluded that processes of phase-slip, involving local disruption of the CDW, are an essential part of the motion.