9701428 Dahm This is a renewal project covering four areas in the study of electrons on liquid helium. We propose a new route to the ripplonic-polaron state, which consists of an electron self- trapped in a surface dimple. We suggest that ripplon-induced weak localization of the electron occurs in the weak scattering limit. As the scattering, controlled by the holding electric field, is increased, a transition to the bound polaron will occur with possibly strong localization as a precursor to the bound state. The mobility of electrons in the low density limit will be studied as a function of holding field, magnetic field, and temperature. We will attempt to observe weak localization by thermal ripplons and the bound polaron state. We further propose to study plasma oscillations of quasi-one-dimensional electron gas formed by confining electrons to helium filled grooves in an insulating substrate. We will also search for viscoelastic modes in the electron fluid and study the pinned electron solid as a function of coupling to pinning centers. %%% This a renewal project to study electrons bound to a liquid helium surface. In such a situation, the bound electrons form a single layer which floats on the surface of helium. This system is the simplest two-dimensional system. It has interesting physical properties and some of its properties are analogs of those which occur in three-dimensional (3D) systems. The parameters controlling these analogs can be varied through a wider range and are more easily controlled than in three dimensions. We propose to study electrons on a helium surface in an attempt to better understand the physics of systems of lower dimensions and the physics of 3D systems which are difficult to probe. Our study will include the spatial localization of electrons by random scattering, analogous to the localization of electrons in some 3D semiconductors. By increasing the scattering rate we expect to find electrons trapped in surface depressions, an analog of electrons trapped in a highly compressible lattice in 3D. We will study the pinned electron crystal which is an analog of 3D sliding charge-density waves. We also propose to study sound in a single rows of electrons in an attempt to understand the physics of one-dimensional systems. ***
