MAGNETOTRANSPORT OF 2D ELECTRONS ON LIQUID-HELIUM IN THE FLUID AND SOLID-PHASES

The magnetoconductivity sigma(B) in the two-dimensional (2D) nondegene rate electron fluid and 2D solid has been analyzed theoretically and i nvestigated 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 ran ge mu B >> 1. At higher fields (depending on the density) sigma(B) is nonmonotonous and displays a minimum. This behavior is due to many-ele ctron effects, which can be described in terms of cyclotron orbit diff usion controlled by an internal fluctuational electric field. The squa red internal field derived from experiments is in good agreement with computer simulations. In the solid phase electron transport becomes st rongly non-linear even for weak driving voltages V-0. Experimentally w e 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 th e first reciprocal lattice vector G(1) of the electron solid. We sugge st that this behaviour is due to to a resonant drag force from the Bra gg-Cerenkov radiation of coherent ripplons by the moving crystal.