61 research outputs found
Cyclotron Resonance Study of the Two-Dimensional Electron Layers and Double-Layers in Tilted Magnetic Fields
The far-infrared absorption in two-dimensional electron layers subject to
magnetic field of general orientation was studied theoretically. The Kubo
formula is employed to derive diagonal components of the magneto-conductivity
tensor of two-dimensional electron single-layers and double-layers. The
parabolic quantum well is used to model a simple single-layer system. Both
single-layer and double-layer systems can be realized in a pair of
tunnel-coupled, strictly two-dimensional quantum wells. Obtained results are
compared to experimental data.Comment: 4 pages, 6 figures, elsart/PHYEAUTH macros; presented on the EP2DS-15
Conference in Nara, Japan. To be published in Physica
Capacitance of Gated GaAs/AlGaAs Heterostructures Subject to In-plane Magnetic Fields
A detailed analysis of the capacitance of gated GaAs/AlGaAs heterostructures
is presented. The nonlinear dependence of the capacitance on the gate voltage
and in-plane magnetic field is discussed together with the capacitance quantum
steps connected with a population of higher 2D gas subbands. The results of
full self-consistent numerical calculations are compared to recent experimental
data.Comment: 4 pages, Revtex. 4 PostScript figures in an uuencoded compressed file
available upon request. Phys. Rev.B, in pres
Inter-layer Hall effect in double quantum wells subject to in-plane magnetic fields
We report on a theoretical study of the transport properties of two coupled
two-dimensional electron systems subject to in-plane magnetic fields. The
charge redistribution in double wells induced by the Lorenz force in crossed
electric and magnetic fields has been studied. We have found that the
redistribution of the charge and the related inter-layer Hall effect originate
in the chirality of diamagnetic currents and give a substantial contribution to
the conductivity.Comment: 7 RevTex pages, 4 figures, appendix added and misprint in Eq. (11)
correcte
Cyclotron effective mass of 2D electron layer at GaAs/AlGaAs heterojunction subject to in-plane magnetic fields
We have found that Fermi contours of a two-dimensional electron gas at
\rmGaAs/Al_xGa_{1-x}As interface deviate from a standard circular shape under
the combined influence of an approximately triangular confining potential and
the strong in-plane magnetic field. The distortion of a Fermi contour manifests
itself through an increase of the electron effective cyclotron mass which has
been measured by the cyclotron resonance in the far-infrared transmission
spectra and by the thermal damping of Shubnikov-de Haas oscillations in tilted
magnetic fields with an in-plane component up to 5 T. The observed increase of
the cyclotron effective mass reaches almost 5 \% of its zero field value which
is in good agreement with results of a self-consistent calculation.Comment: 4 pages, Revtex, figures can be obtained on request from
[email protected]; to appear in Phys. Rev. B (in press). No changes, the
corrupted submission replace
Longitudinal conductivity and transverse charge redistribution in coupled quantum wells subject to in-plane magnetic fields
In double quantum wells electrons experience a Lorentz force oriented
perpendicular to the structure plane when an electric current is driven
perpendicular to the direction of an in-plane magnetic field. Consequently, the
excess charge is accumulated in one of the wells. The polarization of a bilayer
electron system and the corresponding Hall voltage are shown to contribute
substantially to the in-plane conductivity.Comment: 3 pages, 2 figure
Magnetotransport with two occupied subbands in a Si(100) inversion layer
We have studied an electron transport in inversion layers of high-mobility
Si(100) samples. At high electron concentrations and temperatures below 4.2 K,
two series of Shubnikov-de Haas oscillations have been observed. The
temperature damping of the second series oscillations indicates that the second
occupied subband belongs to the first energy level of the fourfold-degenerate
ladder . Samples with two occupied subbans exhibit a strong anomalous
negative magnetoresitance, reaching of a zero field value
at 12 T. The resistance decrease is more pronounced for lower
temperatures and higher electron concentrations. We explain this behaviour by
an increase of the second subband mobility due to the freezing-out of the
scattering of electrons. Based on the measured periods of SdH
oscillations, we conclude that the electrons are distributed inhomogeneously
beneath the sample gate.Comment: 4 pages. RevTex text and 4 PostScript figures in a single
tar-compressed file produced by 'uufiles
Electronic structure of unidirectional superlattices in crossed electric and magnetic fields and related terahertz oscillations
We have studied Bloch electrons in a perfect unidirectional superlattice
subject to crossed electric and magnetic fields, where the magnetic field is
oriented ``in-plane'', i.e. in parallel to the sample plane. Two orientation of
the electric field are considered. It is shown that the magnetic field
suppresses the intersubband tunneling of the Zener type, but does not change
the frequency of Bloch oscillations, if the electric field is oriented
perpendicularly to both the sample plane and the magnetic field. The electric
field applied in-plane (but perpendicularly to the magnetic field) yields the
step-like electron energy spectrum, corresponding to the magnetic-field-tunable
oscillations alternative to the Bloch ones.Comment: 7 pages, 1 figure, accepted for publication in Phys. Rev.
Magnetoresistance and electronic structure of asymmetric GaAs/AlGaAs double quantum wells in the in-plane/tilted magnetic field
Bilayer two-dimensional electron systems formed by a thin barrier in the GaAs
buffer of a standard heterostructure were investigated by magnetotransport
measurements. In magnetic fields oriented parallel to the electron layers, the
magnetoresistance exhibits an oscillation associated with the depopulation of
the higher occupied subband and the field-induced transition into a decoupled
bilayer. Shubnikov-de Haas oscillations in slightly tilted magnetic fields
allow to reconstruct the evolution of the electron concentration in the
individual subbands as a function of the in-plane magnetic field. The
characteristics of the system derived experimentally are in quantitative
agreement with numerical self-consistent-field calculations of the electronic
structure.Comment: 6 pages, 5 figure
Excitonic photoluminescence in symmetric coupled double quantum wells subject to an external electric field
The effect of an external electric field F on the excitonic photoluminescence
(PL) spectra of a symmetric coupled double quantum well (DQW) is investigated
both theoretically and experimentally. We show that the variational method in a
two-particle electron-hole wave function approximation gives a good agreement
with measurements of PL on a narrow DQW in a wide interval of F including
flat-band regime. The experimental data are presented for an MBE-grown DQW
consisting of two 5 nm wide GaAs wells, separated by a 4 monolayers (MLs) wide
pure AlAs central barrier, and sandwiched between Ga_{0.7}Al_{0.3}As layers.
The bias voltage is applied along the growth direction. Spatially direct and
indirect excitonic transitions are identified, and the radius of the exciton
and squeezing of the exciton in the growth direction are evaluated
variationally. The excitonic binding energies, recombination energies,
oscillator strengths, and relative intensities of the transitions as functions
of the applied field are calculated. Our analysis demonstrates that this simple
model is applicable in case of narrow DQWs not just for a qualitative
description of the PL peak positions but also for the estimation of their
individual shapes and intensities.Comment: 5 pages, 4 figures (accepted in Phys. Rev. B
Electronic Structure of Three-Dimensional Superlattices Subject to Tilted Magnetic Fields
Full quantum-mechanical description of electrons moving in 3D structures with
unidirectional periodic modulation subject to tilted magnetic fields requires
an extensive numerical calculation. To understand magneto-oscillations in such
systems it is in many cases sufficient to use the quasi-classical approach, in
which the zero-magnetic-field Fermi surface is considered as a
magnetic-field-independent rigid body in k-space and periods of oscillations
are related to extremal cross-sections of the Fermi surface cut by planes
perpendicular to the magnetic-field direction. We point out cases where the
quasi-classical treatment fails and propose a simple tight-binding
fully-quantum-mechanical model of the superlattice electronic structure.Comment: 8 pages, 7 figures, RevTex, submitted to Phys. Rev.
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