Nonlinear Wigner solid transport over superfluid helium under AC conditions

Nonlinear transport properties of the two-dimensional Wigner solid of surface electrons on superfluid helium are studied for alternating current conditions. For time-averaged quantities like Fourier coefficients, the field-velocity characteristics are shown to be qualitatively different as compared to that found in the DC theory. For a spatially uniform current we found a general solution for the field-velocity relationship which appears to be strongly dependent on the current frequency. If the current frequency is much lower than the ripplon damping parameter, the Bragg-Cherenkov resonances which appear at high enough drift velocities acquire a distinctive saw-tooth shape with long right-side tails independent of small damping. For current frequencies which are close or higher than the ripplon damping coefficient, the interference of ripplons excited at different time intervals results in a new oscillatory (in drift velocity) regime of Bragg-Cherenkov scattering.