Development of a tunnelling model of charge-density-wve depinning

The tunneling model of transport by charge-density waves in quasi-one-dimensional metals has been developed from a close interaction between theory and experiment. Depinning by coherent Zener tunneling of electrons in the CDW condensate in many parallel chains, first applied to NbSe₃,and TaS₃, was suggested by the field dependence of the dc current. In 1981, a program initiated at Illinois to study detection, mixing and harmonic generation was successful in showing that photon-assisted tunneling theory accounts for a wide range phenomena. The only inputs are a scaling parameter and the dc I-V characteristic. Recent measurements by Grüner, Reagor baret al. of θ{symbol}(ω) in the range 1-100 Ghz suggested a modification to account for CDW metals with high pinning frequencies, such as (TaSe₄)₂I and the alloys Ta_1-xNb_xS₃. The dc and low-frequency ac response can be derived from parameters measured at high frequencies. The theory accounts for the "narrow band" noise that accompanies dc current flow and the subharmonic steps of constant current in the dc I-V characteristic measured in the presence of an applied ac.