51 research outputs found
Bond Orientational Order Parameters in the Crystalline Phases of the Classical Yukawa-Wigner Bilayers
We present a study of the structural properties of the crystalline phases for
a planar bilayer of particles interacting via repulsive Yukawa potentials in
the weak screening region. The study is done with Monte Carlo computations and
the long ranged contributions to energy are taken into account with the Ewald
method for quasi-two dimensional systems. Two first order phase transitions
(fluid-solid and solid-solid) and one second order transition (solid-solid) are
found when the surface density is varied at constant temperature. A particular
attention is pay to the characteristics of the crystalline phases by the
analysis of bond orientational order parameters and center-to-center
correlations functions.Comment: 6 pages, 6 figures, 2 table
Bistability and Hysteresis of Intersubband Absorption in Strongly Interacting Electrons on Liquid Helium
We study nonlinear inter-subband microwave absorption of electrons bound to
the liquid helium surface. Already for a comparatively low radiation intensity,
resonant absorption due to transitions between the two lowest subbands is
accompanied by electron overheating. The overheating results in a significant
population of higher subbands. The Coulomb interaction between electrons causes
a shift of the resonant frequency, which depends on the population of the
excited states and thus on the electron temperature . The latter is
determined experimentally from the electron photoconductivity. The
experimentally established relationship between the frequency shift and
is in reasonable agreement with the theory. The dependence of the shift on the
radiation intensity introduces nonlinearity into the rate of the inter-subband
absorption resulting in bistability and hysteresis of the resonant response.
The hysteresis of the response explains the behavior in the regime of frequency
modulation, which we observe for electrons on liquid He and which was
previously seen for electrons on liquid He
Photoresonance and conductivity of surface electrons on liquid ³He
Resonance variations of the in-plane conductivity of surface electrons (SEs) over liquid ³He induced by
microwave (MW) radiation of a fixed frequency are experimentally and theoretically studied for low temperature
scattering regimes (T < 0.5 K). The system was tuned to resonance by varying the amplitude of the
vertical electric field which shifts the positions of SE Rydberg levels. The line-shape change and reversing
of the sign of the effect are found to be opposite to that reported previously for weak vertical electric fields.
A theoretical analysis of conductivity of the SE system heated due to decay of electrons excited to the second
Rydberg level by the MW explains well the line-shape variations observed. It shows also that shifting
the MW resonance into the range of weak vertical fields leads to important qualitative changes in the
line-shape of SE conductivity which are in agreement with observations reported previously
Detecting the Majorana fermion surface state of He-B through spin relaxation
The concept of the Majorana fermion has been postulated more than eighty
years ago; however, this elusive particle has never been observed in nature.
The non-local character of the Majorana fermion can be useful for topological
quantum computation. Recently, it has been shown that the 3He-B phase is a
time-reversal invariant topological superfluid, with a single component of
gapless Majorana fermion state localized on the surface. Such a Majorana
surface state contains half the degrees of freedom of the single Dirac surface
state recently observed in topological insulators. We show here that the
Majorana surface state can be detected through an electron spin relaxation
experiment. The Majorana nature of the surface state can be revealed though the
striking angular dependence of the relaxation time on the magnetic field
direction, where is the angle between the
magnetic field and the surface normal. The temperature dependence of the spin
relaxation rate can reveal the gapless linear dispersion of the Majorana
surface state. We propose a spin relaxation experiment setup where we inject an
electron inside a nano-sized bubble below the helium liquid surface.Comment: 6 pages, 2 figures; reformatted with reference adde
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
Steplike electric conduction in a classical two-dimensional electron system through a narrow constriction in a microchannel
Using molecular dynamics simulation, we investigate transport properties of a
classical two-dimensional electron system confined in a microchannel with a
narrow constriction. As a function of the confinement strength of the
constriction, the calculated conductance in the simulations exhibits steplike
increases as reported in a recent experiment [D. G. Rees et al., Phys. Rev.
Lett. 106, 026803 (2011)]. It is confirmed that the number of the steps
corresponds to the number of stream lines of electrons through the
constriction. We verify that density fluctuation plays a major role in
smoothing the steps in the conductance.Comment: 11 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
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
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