Non-linear behaviour of an electron crystal over liquid helium

Coupled phonon-ripplon oscillations in a two-dimensional electron crystal o n liquid helium have been studied experimentally in a wide interval of driv ing electric fields E. The results obtained for low values of E are in good agreement with theory. Increasing driving electric fields leads to the exc itation of non-axisymmetric modes of coupled phonon-ripplon oscillations. A t high values of E phonon-ripplon resonances disappear. This effect is sugg ested to be explained by plastic deformation and destruction of an electron crystal. (C) 2000 Elsevier Science B.V. All rights reserved.