Studies of melting and sliding charge-density wave conduction of two-dimensional electrons on helium films

In this thesis, we present a new and unique two-dimensional electron system--surface electrons on a thin helium film supported by a dielectric substrate. An order of magnitude higher electronic density was achieved than attainable on bulk helium. In addition, the random substrate impurity potentials were variable.;An experimental cell was designed to measure the transport properties of the surface electrons. Techniques for determining the thickness of a helium film, for measuring the electronic density, for developing an electron source, and for selecting the underlying substrate are discussed.;The phase diagram of a screened Coulomb system was studied. The strength of the electron-electron interaction was varied by changing the electronic density or altering the screening from the image charges in the substrate via the film thickness. The melting temperature was determined by a sharp metal-insulator transition due to the pinning of the Wigner lattice. The melting curve is in quantitative agreement with the Kosterlitz-Thouless theory, within the uncertainty in the screening of the electron-electron interaction.;The crystalization of the electrons forms a natural charge-density-wave with the phase of the lattice pinned by the random potential provided by the spatial variation of the underlying substrate. A series of experiments were performed to study the conduction properties. The dominant features include a field dependence of the conductivity, a frequency dependence of the conductivity, the effects of a superimposed ac field and conduction noise. These phenomena were found to be similar to those observed in Peierls instability induced charge-density-waves in one-dimensional metals. The Coulomb interaction was found to play a large role in the conduction in this two-dimensional electron system.