HELIUM-FILM-INDUCED RETRAPPING TRANSITION IN THE 2-DIMENSIONAL ELECTRON-SYSTEM ABOVE AN UNEVEN SOLID-HYDROGEN SURFACE

A detailed theoretical analysis of the conductivity of surface electro ns above a thin liquid-helium film covering an uneven solid-hydrogen s urface is presented. The pronounced conductivity anomaly which is obse rved during the growth of the helium film is shown to originate from a strong coupling of the electrons to the roughness of the underlying h ydrogen substrate. The observed conductivity anomalies (dip and peak) can be explained quantitatively by a retrapping structural transition within the disordered system of localized charges. We have measured th e effects of varying electron density and discuss the influence of ele ctronic correlation on the conductivity.