ATTENUATION OF PHONON-RIPPLON OSCILLATIONS IN AN ELECTRON CRYSTAL OVER SUPERFLUID HE-3-HE-4 SOLUTIONS

The phonon-ripplon oscillation spectrum of a Wigner crystal with a sur face density 1.3 . 10(9) cm(-2) of electrons over superfluid He-4 and He-3-He-4 solutions is studied in the temperature range 70-600 mK. Mea surements were made in the frequency range 1-20 MHz. It is shown that resonance frequencies are in good agreement with the theoretical estim ates. An analysis of the data shows that the attenuation of capillary waves is not the main mechanism determining the energy losses in a Wig ner crystal. A new technique employing the width of the coupled phonon -ripplon resonances is used to determine the mobility of Wigner crysta ls. (C) 1997 American Institute of Physics.