Sliding charge-density waves. I. dc properties

A classical model of a sliding charge-density wave (CDW) is extended to treat the electrostatic interaction of the CDW with itself, conduction electrons, and the host lattice, as well as with defects. If the CDW is commensurate and the lattice sufficiently coherent, the interaction with the lattice produces, at large voltages, a leading-order nonlinear current of the form ΔI∝-V^-1, which contrasts with ΔI∝-V1/2 due to defects. The effect of a large decrease in the normal conductivity is studied and the defect-contributed ΔI is predicted to be strongly enhanced with decreasing temperature in TaS₃. Interference effects in the commensurate and incommensurate cases are also shown to differ in both detailed shape and temperature dependence. Transport measurements may, therefore, be able to determine whether the CDW's in TaS₃ and NbS₃ are commensurate or incommensurate.