Conductivity of a 2D electron crystal over liquid helium in the region of coupled electron–ripplon resonances

The dependence of the coupled electron–ripplon oscillations spectrum of a 2D electron crystal over liquid helium on the holding electric field is studied at a temperature much lower than the temperature of melting. An analysis of the spectrum near the main resonance (0,1) allowed finding both the real and imaginary components of the crystal conductivity. The imaginary part of the conductivity is shown to be in good agreement with theoretical estimates. At the same time, additional theoretical and experimental studies are necessary to clear up the possible reasons for energy losses in the electron crystal

Nonlinear surface electron transport over liquid helium

We present experimental data and a theoretical analysis of nonequilibrium mobility of surface electrons in liquid helium. The experiments are carried out in the temperature range where electron mobility is limited by electron scattering at surface excitations of liquid helium (ripplons). Holding and driving electric fields of wide ranges are used in measurements. Special attention is paid to the condition of strong holding fields under which hot electrons are confined to the ground surface level. Depending on the relation between the momentum relaxation rate and electron–electron collision frequency, different theoretical approaches are used to describe the nonlinear mobility of surface electrons. The results obtained allow to estimate the range of physical parameters where experimental data can be described by the theory of nonlinear electron transport within the ground surface level

Low-frequency conductivity of a two-dimensional Wigner solid coupled to surface excitations of liquid helium

The line-shape and broadening of coupled phonon-ripplon resonances of Wigner-solid conductivity are studied using the memory function formalism. The analytic properties of the memory function permit coordinating the approximations of the secular equation for the coupled phonon-ripplon modes and the line-broadening of these resonances. Special attention is paid to the description of the strong-coupling regime realized for surface electrons on superfluid helium. For this case it is shown that the line-broadening is much smaller than and the line-shape is different from those found previously using the weak-coupling theory. Different theoretical approaches are compared with available experimental data