ABSTRACT
A broad variety of experiments have been conducted to establish the essential features of the nonlinear conduction caused by the driven collective modes. At low temperatures, with the freeze-out of uncondensed electrons, long range Coulomb interactions become important. These remove the dynamics of internal deformations of the collective mode. A highly oversimplified model—essentially an extension of the harmonic oscillator approach used to describe the ac response—reproduces many of the essential features of the experimental findings on the nonlinear transport process. A simple description of nonlinear transport due to moving density wave condensates neglects the internal dynamics of the mode and treats the dynamics of the rigid condensate, neglecting finite temperature fluctuation effects. The observation demonstrates that the charge-density wave amplitude remains unchanged, and the condensate executes a translational motion in the presence of an applied electric field. The observations on spin density waves are similar to those made on charge density waves.
