Abstract
The characteristics of the spectra of phonon–ripplon oscillations of a two-dimensional electron crystal over liquid helium are investigated at temperatures of 70–500 mK, electron surface densities of (3–12)×108 cm−2, and clamping electric fields of 500–2300 V/cm. Experiments are done in a frequency range of 1–20 MHz. It is shown that at a low level of the exciting signal the characteristics of the spectra are well described by the self-consistent theory of phonon–ripplon oscillations in a crystal. As the exciting signal is increased there is a decrease in the frequencies of the fundamental harmonics of the oscillations, apparently because of a nonlinearity in the electron displacements in the depressions on the liquid helium surface. As the level of the exciting signal is increased further, new modes of phonon–ripplon oscillations begin to be excited in the crystal. These modes are either the theoretically predicted division resonances arising at large electron displacements or the asymmetric modes caused...
Published Version
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