MAGNETORESISTANCE IN 2D ELECTRONS ON LIQUID-HELIUM - MANY-ELECTRON VERSUS SINGLE-ELECTRON KINETICS

The magnetoresistance rho(xx) of two-dimensional electrons, density n, on liquid helium was measured up to the quantum limit, near 1 K where the scattering is due to He-4 vapor atoms. Temperature- and density-d ependent positive magnetoresistance was observed. Many-electron theory is presented that ''restores'' the Drude formalism for HBARomega(p) < < kT << e2n1/2/epsilon0 [omega(p)=(e2n3/2/2epsilon0m)1/2 is the plasma frequency] for classically strong magnetic fields, and shows large ma gnetoresistance in higher fields, in agreement with the data. The cros sover to single-electron kinetics at the highest fields is discussed.