Yu. Z. Kovdrya

Carrier transport and localization in a one-dimensional electronic system over liquid helium

The carrier mobility in a nearly one-dimensional electronic system over liquid helium is measured. One-dimensional conducting channels are created by using the curvature of the surface of liquid helium covering a profiled dielectric substrate and applying a clamping electric field, which holds the electrons on the bottom of the liquid troughs. Measurements are made in a temperature interval of 0.5–1.6 K at linear densities in the range (0.5–2.5)×104 cm−1 at a generator voltage of 2–200 mV. It is shown that for a clean substrate the mobility of the electrons is governed by their interaction with helium atoms in the vapor and with ripplons; the results of the measurements are in satisfactory agreement with a theoretical calculation that assumes no localization. It is found that for substrates carrying a charge or having defects on the surface, the electron mobility decreases in comparison with the value for a clean substrate, and at temperatures T<1 K is either practically independent of temperature or decr...

Quantum transport of surface electrons over liquid helium in magnetic field

The magnetoconductivity Σxx of surface electrons over liquid helium at electron densities (1–9) × 108 cm−2 is measured at temperatures down to 0.5 K and magnetic fields H up to 25 kOe. Σxx is shown to decrease with increasing H. For rather high temperatures and low magnetic fields dependence Σxx−1 on H displays a classical behavior, but as the temperature is reduced or H is increased, a transition to the quantum magnetotransport regime occurs. It is shown that Σxx decreases at lowering temperature, passes through a minimum and then slightly increases in the region of electron-ripplon scattering. The measured data are in good agreement with the theoretical results taking into account the preferable contribution of electron scattering on ripplons with wavelength near magnetic length. At the region of electron crystal Σxx is weakly dependent on T. At low magnetic field Σxx−1 increases with H linearly and, at H>17kOe, Σxx−1 ~ H1.5.

Weak localization effects in a quasi-one-dimensional electron system over liquid helium

Magnetoresistance ρxx measurements are performed for a quasi-one-dimensional electron system over liquid helium in the gas-scattering region (the temperature range 1.3–2.0 K). The measurements show that, as the magnetic field increases, the magnetoresistance ρxx first decreases and then passes through a minimum and increases according to the law ρxx∼B2. It is suggested that the negative magnetoresistance observed in the experiment is caused by the weak localization effects. The results of the experiment are in qualitative agreement with the theoretical model describing the weak localization effects in a one-dimensional nondegenerate electron system.

One-dimensional and zero-dimensional electron systems on liquid helium (Review)

A review of the experimental and theoretical research on one-dimensional and zero-dimensional electron systems localized near a liquid helium surface is given. The properties of the electronic states on a flat liquid helium surface, including the surface of thin helium layers, are briefly considered. Ways of realizing one-dimensional and zero-dimensional electron systems and the results of experimental and theoretical studies of their properties are discussed. Experiments on the investigation of localization processes in quasi-one-dimensional electron systems are described. Collective effects in systems of this kind are considered, and the possibilities for the use of low-dimensional electron systems on the surface of liquid helium for creating electronic devices and quantum computers are explored.

Kinetic properties of surface electrons over liquid helium under strong electron-electron interaction

The mobility μ and lifetime of ground-level electrons τ⊥ are studied experimentally in a two-dimensional electron system at the surface of liquid helium at temperatures of0.4 to1.4 K and charge concentrations of (2.8–12.0) × 108 cm−2. It is shown that for fairly low temperature and high concentration where the frequency of interelectronic collisions is much higher than that of electron-ripplon ones, the so-called complete control condition is realized in the electron system, i.e., when the average drift velocity of electrons and the effective electron temperature can be introduced. This model is found to describe well the kinetic properties of surface electrons in the range of charge concentrations up to 4×108 cm−2, where the one-particle approach is no longer applicable. For the value of parameter Γ=e2(πns)1/2/T=47 that corresponds to a strong electron-electron interaction, the lifetime τ⊥ is found to increase sharply and the short-range order typical of a liquid state appears in the two-dimensional electron layer.

LINEAR ELECTRON CHAINS ON THE LIQUID HELIUM SURFACE : CARRIER TRANSPORT

The unique system - linear electron chains on the liquid helium surface was realized experimentally for the first time. The system was realized using curvature of the liquid helium surface film covering a profiled substrate with a small dielectric constant and a pressing electric field holding electrons in the liquid channels. The conductivity of carriers in linear electron chains and magnetoresistance of a quasi-one-dimensional system have been measured in the temperature range 0.5 - 1.8 K in holding electric fields up to 1 kV/cm. The transport properties of the system depend on the substrate cleanness. For a clean system the electron mobility increases with decreasing temperature, the data are in good agreement with the existing theory which describes transport properties in a one-dimensional electron system without localization. Charging of substrate leads to the localization process in electron chains. It has been shown that in the absence of localization magnetoresistance of a quasi-one-dimensional system on liquid helium in the region of ripplon scattering increases with increasing magnetic field.

Carrier transport in quasi-one-dimensional electron systems over liquid helium under strong localization conditions

The conductivity of carriers in a quasi-one-dimensional electron system over liquid helium is measured in the temperature interval 0.5−1.9 K in confining electric fields up to 4 kV/cm at a frequency of 1.1 MHz. Quasi-one-dimensional channels were created by using an optical diffraction grating covered with a thin helium layer. The carrier conductivity decreases exponentially with temperature T, and the activation energy is of the order of a few degrees, thus pointing towards localization of electrons in a quasi-one-dimensional electron system. As the thickness of the helium layer covering the grating is increased, a departure from a mono exponential dependence is observed at T<0.8 K, which indicates that quantum effects begin to play an active role in electron mobility at these temperatures. An analysis of the obtained results leads to the assumption that under localization conditions, quasi-one-dimensional electron systems may contain two branches of the optical mode of plasma oscillations, viz., a high-...

Mobility and localization of charge carriers in a quasi-one-dimensional electron system over liquid helium

The conductivity and mobility of charge carriers in a quasi-one-dimensional electron system over liquid helium is measured in the temperature range 0.5–1.8 K in confining electric fields up to 2.5 kV/cm. The system of quasi-one-dimensional channels is constructed by using high-quality optical diffraction gratings arranged at a certain height h over liquid helium which fill the grooves of the gratings, thus creating one-dimensional liquid channels. It is shown that the electron mobility decreases with increasing h, the value of the mobility being smaller than the corresponding value for bulk helium. As the temperature decreases, the mobility increases, passes through a peak, and then decreases. The observed effects can be explained by localization of charge carriers in quasi-one-dimensional electron systems.

Evidence for the edge magnetoplasmon “Acoustic” mode in an electron layer over liquid helium

The spectrum of new modes of edge magnetoplasmons (EMP) in an electron layer over liquid helium was studied. The experiments were carried out in the temperature range 0.5–0.7 K at frequencies 0.87–1 MHz and electron density (1.5–3.5) ⋅ 1012 m−2 in a magnetic field up to 0.5 T. Besides conventional edge magnetoplasmons and the EMP mode connected with the displacement of the electron sheet boundary, a new “ acoustic” edge magnetoplasmon mode was observed in an electron layer over liquid helium for the first time. Spectrum of all three types of the magnetoplasmon modes are compared with the existing theories.

Anomalous charge transport in a quasi-one-dimensional electron system over liquid helium

The conductivity σ in a quasi-one-dimensional electron system over liquid helium is measured in the temperature interval 0.5–1.7 K over a wide range of electron densities n. It is shown that the quantity σ/ne (e is the charge of the electron) initially increases with decreasing temperature and then, after passing through a maximum, begins to decline for T≈1 K. In this temperature region the value of σ/ne, above a certain value of the drift potential Vd, decreases with increasing Vd. It is conjectured that the anomalous charge transport observed in this study is due either to spatial ordering of the electrons in the quasi-one-dimensional channels or to the formation of many-electron polarons in the nonuniform potential along the channels.