MAGNETOCONDUCTIVITY OF 2-DIMENSIONAL ELECTRONS ON LIQUID-HELIUM - EXPERIMENTS IN THE FLUID-PHASE

The magnetoconductivity sigma(B) of two-dimensional electrons on liqui d helium was measured from 0.25 to 1.3 K in the electron fluid phase i n magnetic fields up to 8 T. In low magnetic fields B, sigma(0)/sigma( B)= 1+(mu B)(2) as in the Drude model, where mu is the zero-field mobi lity due to scattering by He-4 vapor atoms and ripplons, even for mu B much greater than 1. The values of mobility are in good agreement wit h previous measurements and with calculations for a correlated electro n fluid. At higher fields, sigma(0)/sigma(B) deviates from the Drude m odel and becomes density dependent due to many-electron effects. Only at the highest fields, or the lowest densities, does sigma(B) approach the theoretical single-particle magnetoconductivity. For both vapor-a tom and ripplon scattering the results are in good agreement with a mi croscopic many-electron theory in which the diffusion of the cyclotron orbits is controlled by the internal fluctuational electric fields. T he density and temperature dependence of these internal fields derived from the experiments are in excellent agreement with Monte Carlo simu lations.