Two-fraction electron system on a thin helium film

A systematic theoretical investigation of microwave absorption of 2-dimensi onal electron systems above a thin helium film in the presence of a cyclotr on resonance magnetic field is presented. To explain the measured data, a t wo-fraction structure of the electron system is introduced. One component c orresponds to the free electron motion, the second one takes into account e lectron localization near the potential minimum caused by the roughness of the substrate. Within this model the general dependence of microwave absorp tion becomes understandable. The details of the observed cyclotron resonanc e line-shift are discussed.