Dynamical Transition in the Wigner Solid on a Liquid Helium Surface

We have observed a dynamical transition in the Wigner solid on liquid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$. The ac Corbino conductivity ${\sigma }_{\mathrm{xx}}$ jumps abruptly at certain input voltage and shows hysteretic behavior. The threshold input voltage $V_{\mathrm{th}}$ has dependences on the magnetic field $B$ perpendicular to the surface, frequency $\omega$, electron density $n_s$, and electric field $E_{\perp }$ as $V_{\mathrm{th}}\propto B^{-0.8\mathrm{}}{\omega }^{-1\mathrm{}}{n}_s^{1.5}{E}_{\perp }$. We attribute the conductivity jump to the collective sliding of the electrons out of the periodic deformation of the He surface.