A systematic theoretical investigation of microwave absorption of 2-dimensional electron systems above a thin helium film in the presence of a cyclotron resonance magnetic field is presented. To explain the measured data, a two-fraction structure of the electron system is introduced. One component corresponds to the free electron motion, the second one takes into account electron localization near the potential minimum caused by the roughness of the substrate. Within this model the general dependence of microwave absorption becomes understandable. The details of the observed cyclotron resonance line-shift are discussed.

Low-frequency magnetoconductivity measurements of two-dimensional surface electrons on liquid He-4 under cyclotron resonance conditions are reported here. At relatively low-electron densities, the cyclotron-resonance-induced conductivity line shape is a phenomenological combination of two resonances, which can be separated by fitting. The resonance which shows a decrease of the effective scattering Lime tau(eff) with increasing driving field is studied here: the observed shift of the resonance, the resonance linewidth and the effective scattering frequency. It is found that the extracted tau(eff) has a similar electric driving field dependence as published experimental results from zero-magnetic field, de time-of-flight measurements.

We have observed strong narrowing of the quantum cyclotron resonance (CR) linewidth of surface electrons on liquid helium, which is caused by the many-electron fluctuational field. In the reported experiment, the amplitude of the internal fluctuational electric field was varied by changing the electron density (linear CR regime) and electron temperature (nonlinear CR regime). The observed Coulombic effect is interpreted as an inelastic suppression of the collision broadening of Landau levels due to the ultra-fast drift velocities of the electron orbits in the strong fluctuational many-electron field.

We report results of experimental and theoretical studies of cyclotron resonance (CR) absorption from a strongly interacting nondegenerate two-dimensional electron liquid with extremely narrow Landau levels realized on the free surface of liquid helium. We found that the main many-electron effect on the quantum CR originates from the ultrafast fluctuational motion of electron orbit centers, causing inelastic scattering in the moving frames. This effect is described by means of the memory function formalism, employing a many-electron approximation for the electron dynamic structure factor (DSF). Remarkably, the Coulombic effect leads to a narrowing of Landau levels and at the same time produces a strong broadening of the electron DSF and the relaxation kernel of the dynamic conductivity. This explains the observed transformation of the CR line shape and the successive narrowing and broadening of the CR linewidth with the increase of the electron density. It is shown that the Coulomb narrowing and broadening of the CR data respond differently to a change of the resonant frequency in accordance with the concept proposed.

We have observed a narrowing of the linear cyclotron resonance linewidth with an increase in the density of surface electrons on liquid helium in the electron-vapor atom scattering regime. The effect changes sign at densities n(s) > 1.7 X 10(8) cm(-2). The data are interpreted as a Coulombic effect on the Landau level width produced by a strong fluctuating electric field. [S0031-9007(99)08755-4].

To eliminate locally a strong quasiuniform many-electron field and to restore the applicability of the self-consistent approximation, we propose the transcription into frames moving ultrafast along with each orbit center. This allows us to find new formulas for the magnetoconductivity and collision broadening of Landau levels affected by strong Coulomb interaction. As a test for the new theory, in the same experiment, we have measured the magnetoconductivity and cyclotron resonance linewidth of surface electrons on liquid helium. Obtained data are in good agreement with the theoretical concept.

A promising way to investigate 2D contact phenomena is proposed. This method is based on the idea of depositing surface state electrons (SSE) on a thin layer of liquid helium covering the surface of a solid sample containing a 2D charge carrier system. The density of SSE adjusts to screen contact-induced perturbations of the electrostatic potential across the sample. As a result, the helium layer thickness varies due to the variation of the electrostatic pressure, thus providing a map. This map may be read off interferometrically by a technique already employed for the investigation of multi-electron dimples on helium. We have realized this mapping for a structured electrode as a test sample to demonstrate the resolution of the method.

A novel way to investigate perturbations of the electrostatic potential across a sample surface is presented, aiming at application in 2D contact phenomena. The idea is to deposit surface state electrons (SSE) on a thin layer of liquid helium covering the surface of a solid state sample. The density of the SSE adjusts to screen perturbations of the electrostatic potential across the sample. As a result, the helium layer thickness varies due to the variation of the electrostatic pressure, thus providing a map. This map may be read interferometrically by a technique already employed for the investigation of multi-electron dimples on helium. We realized this mapping for a structured metal electrode as a test sample to investigate the resolution of the method.

A helium film suspended between elevations on a substrate forms an excellent surface for a two-dimensional electron gas. With the structure on the substrate a quasi one-dimensional electron system can be created. Experiments probing the electrical transport properties of this system have raised questions about the suspended helium film itself. We report measurements of the suspended film using interferometry. The profile is mapped out as a function of the bulk helium level beneath the substrate. By measuring the electron signal simultaneously the relation between the signal and the film profile can be obtained.

A promising way to investigate 2D contact phenomena is proposed. This method is based on the idea of depositing surface state electrons (SSE) on a thin layer of liquid helium covering the surface of a solid sample containing a 2D-charge carrier system. The density of SSE adjusts to screen contact-induced perturbations of the electrostatic potential across the sample. As a result, the helium layer thickness varies due to the variation of the electrostatic pressure, thus providing a map. This map may be read off interferometrically by a technique already employed for the investigation of multi-electron dimples on helium. We have realized this mapping for a structured electrode as a test sample to demonstrate the resolution of the method.

Surface electrons (SE) prepared on helium films of thickness d are supposed to undergo a transition to the polaronic state when the corresponding binding energy lambda(b) similar to d(-4) is close to or larger than k(B)T. Although the polaron has been observed recently, no clear transition was seen so far. In this paper we want to present magnetotransport measurements carried out at rather high temperatures (T > 1.2 K) to avoid the Wigner crystallization for a wide range of electron densities (5 x 10(8) cm(-2) < n(e) < 7 x 10(9) cm(-2)) showing this transition to the polaronic state: The experimental evidence is demonstrated in zero-field mobility measurements versus d and also shown in the corresponding magnetotransport measurements up to 10T below and above the transition. (C) 1998 Elsevier Science B.V. All rights reserved.

We report preliminary results of a cyclotron resonance study of surface electrons (SE) on saturated helium films covering a PMMA substrate at T > 1 K. The real and imaginary parts of the dielectric response ∈(k,ω) of the SE are measured at fixed k and ω in B-fields up to 10 T in a 12 GHz cavity. The cyclotron resonance of the SE is determined at different helium film thicknesses dHeand at various electron densities. At small dHewe find significant anomalies in the cyclotron resonance lineshape and position. As dHeincreases the lineshape becomes progressively more symmetric and its peak moves towards the cyclotron field value expected for a free electron. To fit these data we have modified the classical Drude expression, introducing two different relaxation times for the low and high B-field regions. The phenomenological formulas fit the data quite well. A systematic theoretical analysis of these results is in progress.

A change in the shape of a charged surface of liquid hydrogen and helium — the formation of a solitary wave (a positively charged hump for hydrogen and a negatively charged dimple for helium)-is observed in an electric field exceeding a critical value under conditions of total compensation of the applied field by the surface charge.