87 research outputs found
Wave excitations of drifting two-dimensional electron gas under strong inelastic scattering
We have analyzed low-temperature behavior of two-dimensional electron gas in
polar heterostructures subjected to a high electric field. When the optical
phonon emission is the fastest relaxation process, we have found existence of
collective wave-like excitations of the electrons. These wave-like excitations
are periodic in time oscillations of the electrons in both real and momentum
spaces. The excitation spectra are of multi-branch character with considerable
spatial dispersion. There are one acoustic-type and a number of optical-type
branches of the spectra. Their small damping is caused by quasi-elastic
scattering of the electrons and formation of relevant space charge. Also there
exist waves with zero frequency and finite spatial periods - the standing
waves. The found excitations of the electron gas can be interpreted as
synchronous in time and real space manifestation of well-known
optical-phonon-transient-time-resonance. Estimates of parameters of the
excitations for two polar heterostructures, GaN/AlGaN and ZnO/MgZnO, have shown
that excitation frequencies are in THz-frequency range, while standing wave
periods are in sub-micrometer region.Comment: 26 pages and 6 figure
Rotating bi-electron in two-dimensional systems with mexican-hat single-electron energy dispersion
A number of novel two-dimensional materials and nanostructures demonstrate
complex single-electron energy dispersion, which is called the mexican-hat
dispersion. In this paper, we analyze interaction of a pair of electrons with
such an energy dispersion. We show that relative motion of the electron pair is
of a very peculiar character. For example, the real space trajectories
corresponding to electron-electron scattering can have three reversal points,
reversal points at non-zero radial momentum and other unusual features. Despite
the repulsive Coulomb interaction, two electrons can be coupled forming a
composite quasi-particle - the bi-electron. The bi-electron corresponds to
excited states of the two-electron system. Because the bi-electron coupled
states exist in continuum of extended (free) states of the electron pair, these
states are quasi-resonant and have finite times of life. We found that rotating
bi-electron is a long-living composite quasi-particle. The rotating
bi-electrons can be in motion. For slowly moving bi-electrons, we determined
the kinetic energy and the effective mass. Due to strongly nonparabolic energy
dispersion, the translational motion of the bi-electron is coupled to its
internal motion. This results in effective masses dependent on quantum states
of the bi-electron. In the paper, properties of the bi-electron are illustrated
for the example of bigraphene in a transverse electric field.Comment: 13 pages, 4 figure
Coherent patterns and self-induced diffraction of electrons on a thin nonlinear layer
Electron scattering on a thin layer where the potential depends
self-consistently on the wave function has been studied. When the amplitude of
the incident wave exceeds a certain threshold, a soliton-shaped brightening
(darkening) appears on the layer causing diffraction of the wave. Thus the
spontaneously formed transverse pattern can be viewed as a self-induced
nonlinear quantum screen. Attractive or repulsive nonlinearities result in
different phase shifts of the wave function on the screen, which give rise to
quite different diffraction patterns. Among others, the nonlinearity can cause
self-focusing of the incident wave into a ``beam'', splitting in two ``beams'',
single or double traces with suppressed reflection or transmission, etc.Comment: RevTex, 4 pages, epsf.sty to insert figures, to appear in Phys.Rev.
Self-consistent theory of shot noise in nondegenerate ballistic conductors
A self-consistent theory of shot noise in ballistic two-terminal conductors
under the action of long-range Coulomb correlations is presented. Analytical
formulas for the electron distribution function and its fluctuation along the
conductor, which account for the Coulomb correlations, have been derived. Based
upon these formulas, the current-noise reduction factor has been obtained for
biases ranging from thermal to shot-noise limits as dependent on two
parameters: the ratio between the length of the sample and the Debye screening
length \lambda=d/L_D and the applied voltage qU/k_BT. The difference with the
formulas for a vacuum diode is discussed.Comment: 21 pages, 11 figs, minor change
Cerenkov generation of high-frequency confined acoustic phonons in quantum wells
We analyze the Cerenkov emission of high-frequency confined acoustic phonons
by drifting electrons in a quantum well. We find that the electron drift can
cause strong phonon amplification (generation). A general formula for the gain
coefficient, alpha, is obtained as a function of the phonon frequency and the
structure parameters. The gain coefficient increases sharply in the short-wave
region. For the example of a Si/SiGe/Si device it is shown that the
amplification coefficients of the order of hundreds of 1/cm can be achieved in
the sub-THz frequency range.Comment: 4 pages, 2 figures. Submitted to AP
Electric Current and Noise in Long GaN Nanowires in the Space-Charge Limited Transport Regime
We studied electric current and noise in planar GaN nanowires (NWs). The
results obtained at low voltages provide us with estimates of the depletion
effects in the NWs. For larger voltages, we observed the space-charge limited
current (SCLC) effect. The onset of the effect clearly correlates with the NW
width. For narrow NWs the mature SCLC regime was achieved. This effect has
great impact on fluctuation characteristics of studied NWs. At low voltages, we
found that the normalized noise level increases with decreasing NW width. In
the SCLC regime, a further increase in the normalized noise intensity (up to
1E4 times) was observed, as well as a change in the shape of the spectra with a
tendency towards slope -3/2. We suggest that the features of the electric
current and noise found in the NWs are of a general character and will have an
impact on the development of NW-based devices.Comment: 12 pages, 4 figures in Fluctuation and Noise Letters (2017
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