Microwave study of screened two-dimensional electron crystals on helium films

Abstract

We report investigations at microwave frequencies on surface-state electrons (SSE) which were supported by helium films adsorbed on different polymer substrates at temperatures above 1 K. The real and imaginary parts of the dielectric response (Formula presented) of the SSE were measured at fixed (Formula presented) and ω inside a 10 GHz microwave cavity. The solidification of the two-dimensional electron crystal was detected by a kink occurring simultaneously in both components of (Formula presented) as the electron density was slowly increased at constant temperature. The influence of the dielectric substrate on such a freezing transition has been measured at different temperatures and at various helium-film thicknesses. The results are found to be in good agreement with existing theories. This work represents the first systematic study of a screened two-dimensional electron crystal on helium. © 1997 The American Physical Society.