26 research outputs found
Continuum elasticity theory of edge excitations in a two-dimensional electron liquid with finite range interactions
We make use of continuum elasticity theory to investigate the collective
modes that propagate along the edge of a two-dimensional electron liquid or
crystal in a magnetic field. An exact solution of the equations of motion is
obtained with the following simplifying assumptions: (i) The system is {\it
macroscopically} homogeneous and isotropic in the half-plane delimited by the
edge (ii) The electron-electron interaction is of finite range due to screening
by external electrodes (iii) The system is nearly incompressible. At
sufficiently small wave vector we find a universal dispersion curve independent of the shear modulus. At larger wave vectors the dispersion
can change its form in a manner dependent on the comparison of various length
scales. We obtain analytical formulas for the dispersion and damping of the
modes in various physical regimes.Comment: 3 figure
Plasma dispersion of multisubband electron systems over liquid helium
Density-density response functions are evaluated for nondegenerate
multisubband electron systems in the random-phase approximation for arbitrary
wave number and subband index. We consider both quasi-two-dimensional and
quasi-one- dimensional systems for electrons confined to the surface of liquid
helium. The dispersion relations of longitudinal intrasubband and transverse
intersubband modes are calculated at low temperatures and for long wavelengths.
We discuss the effects of screening and two-subband occupancy on the plasmon
spectrum. The characteristic absorption edge of the intersubband modes is
shifted relatively to the single-particle intersubband separation and the
depolarization shift correction can be significant at high electron densities
Temperature-dependent energy levels of electrons on liquid helium
We present measurements of the resonant microwave absorption by the Rydberg
energy levels of surface state electrons on the surface of superfluid liquid
helium, in the frequency range 165 - 220 GHz. The resonant frequency was
strongly temperature dependent from 0.1 to 2 K. The experiments are in
agreement with recent theoretical calculations of the renormalisation of the
electron energy levels due to zero-point and thermal ripplons, analogous to a
condensed matter Lamb shift. The temperature-dependent contribution to the
linewidth for excitation to the first excited state at 189.6 GHz is compared
with other measurements and theoretical predictions.Comment: 24 pages, 9 figure
Nonequilibrium phenomena in high Landau levels
Developments in the physics of 2D electron systems during the last decade
have revealed a new class of nonequilibrium phenomena in the presence of a
moderately strong magnetic field. The hallmark of these phenomena is
magnetoresistance oscillations generated by the external forces that drive the
electron system out of equilibrium. The rich set of dramatic phenomena of this
kind, discovered in high mobility semiconductor nanostructures, includes, in
particular, microwave radiation-induced resistance oscillations and
zero-resistance states, as well as Hall field-induced resistance oscillations
and associated zero-differential resistance states. We review the experimental
manifestations of these phenomena and the unified theoretical framework for
describing them in terms of a quantum kinetic equation. The survey contains
also a thorough discussion of the magnetotransport properties of 2D electrons
in the linear response regime, as well as an outlook on future directions,
including related nonequilibrium phenomena in other 2D electron systems.Comment: 60 pages, 41 figure
Decay of excited surface electron states in liquid helium and related relaxation phenomena induced by short-wavelength ripplons
Decay rates of excited surface electron states on liquid helium are theoretically studied for different electron confinement potentials and in the presence of quantizing magnetic field. Contributions of both one-ripplon and two-ripplon scattering processes are analyzed. Regarding the decay rate of the first excited surface level (l=2), two-ripplon emission of short wave-length capillary waves is shown to dominate the conventional one-ripplon scattering in two distinct cases: the ambient temperature is low enough, or the surface state excitation energy Δ₂–Δ₁ does not match an excitation energy of the in-plane motion quantized under a strong magnetic field or in a quantum dot. In these cases, magnetic field and confinement cannot essentially reduce the decay rate which is of order of 10⁶ s⁻¹ and does not depend on temperature. Importance of these findings for a microwave resonance experiment is discussed
Microwave absorption saturation and decay heating of surface electrons on liquid helium
The microwave (MW) resonance absorption and decay heating of surface electrons (SEs) on liquid ⁴He
are theoretically studied for the vapor atom scattering regime. The decay heating is shown to be an essential
occurrence of a MW resonance experiment appearing even at low excitation rates. It strongly affects the occupancies
of surface levels and the broadening of resonance lines long before the absorption suturation condition
is reached. Contrary to the model of cold SEs usually used for description of the MW resonance, the
new theory leads to MW absorption saturation when only a very small fraction of electrons (less than 10%) is
left on the ground and the first excited levels
Bistable transport properties of a quasi-one-dimensional Wigner solid on liquid helium under continuous driving
Cyclotron resonance of a two-dimensional Wigner solid
Cyclotron resonance absorption from a two-dimensional electron solid formed on a free surface of liquid helium is analyzed by means of the memory function formalism. The presence of the low-frequency phonon mode of the Wigner solid in a strong magnetic field is shown to broaden significantly the electron dynamical structure factor (DSF) as a function of frequency, strengthening the contribution from multi-phonon emission terms of the high-frequency mode. Thus in most cases the linewidth is formed by nonlinear terms of the DSF expansion in the cyclotron motion factor exp (-iwct) rather than by the linear terms analyzed previously. The inclusion of all these multi-phonon terms changes the sign of the many-electron effect and agrees well with available experimental data, eliminating the discrepancy between theory and experiment.
Cyclotron resonance absorption from a two-dimensional electron solid formed on a free surface of liquid helium is analyzed by means of the memory function formalism. The presence of the low-frequency phonon mode of the Wigner solid in a strong magnetic field is shown to broaden significantly the electron dynamical structure factor (DSF) as a function of frequency, strengthening the contribution from multiphonon emission terms of the high-frequency mode. Thus in most cases the linewidth is formed by nonlinear terms of the DSF expansion in the cyclotron motion factor exp(−iωct) rather than by the linear terms analyzed previously. The inclusion of all these multiphonon terms changes the sign of the many-electron effect and agrees well with available experimental data, eliminating the discrepancy between theory and experiment