Magnetotransport of 2D electrons on liquid helium in the fluid and solid phases

The magnetoconductivity sigma(B) in the two-dimensional (2D) nondegenerate electron fluid and 2D solid has been analyzed theoretically and investigated experimentally, from 60 mK to 1.3 Ii in magnetic fields B up to 8 Tesla. In the fluid phase, sigma(B) is described by the Drude model in weak to moderately strong classical fields, including the range mu B >> 1. At higher fields (depending on the density) sigma(B) is nonmonotonous and displays a minimum. This behavior is due to many-electron effects, which can be described in terms of cyclotron orbit diffusion controlled by an internal fluctuational electric field. The squared internal field derived from experiments is in good agreement with computer simulations. In the solid phase electron transport becomes strongly non-linear even for weak driving voltages V-0. Experimentally we determine, from the losses, the effective AC Corbino conductivity at a frequency f. We find that sigma(B) proportional to fV(0)/B for V-0 below some threshold voltage V-c. In this region the Hall velocity nu(H) approaches the ripplon phase velocity v(1) = omega(G(1))/G(1) at the first reciprocal lattice vector G(1) of the electron solid. We suggest that this behaviour is due to to a resonant drag force from the Bragg-Cerenkov radiation of coherent ripplons by the moving crystal.