BRAGG-CHERENKOV SCATTERING AND NONLINEAR CONDUCTIVITY OF A 2-DIMENSIONAL WIGNER CRYSTAL

We show that the conductivity of 2D Wigner crystals displays strong no nlinearity. It arises from coherent many-electron Cherenkov emission o f surface waves in the substrate (e.g., ripplons on helium) with the w ave vectors q close to the reciprocal lattice vectors G of the electro n solid. The rate of such Bragg-Cherenkov scattering sharply increases with the Wigner crystal velocity v as v . G approaches the surface wa ve frequency omega(G). The results are compared with recent experiment s.