174 research outputs found
Quantum effects in linear and non-linear transport of T-shaped ballistic junction
We report low-temperature transport measurements of three-terminal T-shaped
device patterned from GaAs/AlGaAs heterostructure. We demonstrate the mode
branching and bend resistance effects predicted by numerical modeling for
linear conductance data. We show also that the backscattering at the junction
area depends on the wave function parity. We find evidence that in a non-linear
transport regime the voltage of floating electrode always increases as a
function of push-pull polarization. Such anomalous effect occurs for the
symmetric device, provided the applied voltage is less than the Fermi energy in
equilibrium
Nucleation at the phase transition near 40 C in MnAs nanodisks
The phase transition near 40 C of both as grown thin epitaxial MnAs films prepared by molecular beam epitaxy on GaAs 001 and nanometer scale disks fabricated from the same films is studied. The disks are found to exhibit a pronounced hysteresis in the temperature curve of the phase composition. In contrast, supercooling and overheating take place far less in the samples of continuous layers. These phenomena are explained in terms of the necessary formation of nuclei of the other phase in each of the disks independent from each other. The influence of the elastic strains in the disks is reduced considerabl
Influence of the single-particle Zeeman energy on the quantum Hall ferromagnet at high filling factors
In a recent paper [B. A. Piot et al., Phys. Rev. B 72, 245325 (2005)], we
have shown that the lifting of the electron spin degeneracy in the integer
quantum Hall effect at high filling factors should be interpreted as a
magnetic-field-induced Stoner transition. In this work, we extend the analysis
to investigate the influence of the single-particle Zeeman energy on the
quantum Hall ferromagnet at high filling factors. The single-particle Zeeman
energy is tuned through the application of an additional in-plane magnetic
field. Both the evolution of the spin polarization of the system and the
critical magnetic field for spin splitting are well described as a function of
the tilt angle of the sample in the magnetic field.Comment: Published in Phys. Rev.
Spin splitting in a polarized quasi-two-dimensional exciton gas
We have observed a large spin splitting between "spin" and
heavy-hole excitons, having unbalanced populations, in undoped GaAs/AlAs
quantum wells in the absence of any external magnetic field. Time-resolved
photoluminescence spectroscopy, under excitation with circularly polarized
light, reveals that, for high excitonic density and short times after the
pulsed excitation, the emission from majority excitons lies above that of
minority ones. The amount of the splitting, which can be as large as 50% of the
binding energy, increases with excitonic density and presents a time evolution
closely connected with the degree of polarization of the luminescence. Our
results are interpreted on the light of a recently developed model, which shows
that, while intra-excitonic exchange interaction is responsible for the spin
relaxation processes, exciton-exciton interaction produces a breaking of the
spin degeneracy in two-dimensional semiconductors.Comment: Revtex, four pages; four figures, postscript file Accepted for
publication in Physical Review B (Rapid Commun.
Phase study of oscillatory resistances in microwave-irradiated- and dark- GaAs/AlGaAs devices: Indications of a new class of integral quantum Hall effect
We report the experimental results from a dark study and a photo-excited
study of the high mobility GaAs/AlGaAs system at large filling factors, .
At large-, the dark study indicates several distinct phase relations
("Type-1", "Type-2", and "Type-3") between the oscillatory diagonal- and Hall-
resistances, as the canonical Integral Quantum Hall Effect (IQHE) is manifested
in the "Type-1" case of approximately orthogonal diagonal- and Hall resistance-
oscillations. Surprisingly, the investigation indicates quantum Hall plateaus
also in the "Type-3" case characterized by approximately "anti-phase" Hall- and
diagonal- resistance oscillations, suggesting a new class of IQHE.
Transport studies under microwave photo-excitation exhibit radiation-induced
magneto-resistance oscillations in both the diagonal, , and
off-diagonal, , resistances. Further, when the radiation-induced
magneto-resistance oscillations extend into the quantum Hall regime, there
occurs a radiation-induced non-monotonic variation in the amplitude of
Shubnikov-de Haas (SdH) oscillations in \textit{vs}. B, and a
non-monotonic variation in the width of the quantum Hall plateaus in .
The latter effect leads into the vanishing of IQHE at the minima of the
radiation-induced oscillations with increased photo-excitation. We
reason that the mechanism which is responsible for producing the non-monotonic
variation in the amplitude of SdH oscillations in under
photo-excitation is also responsible for eliminating, under photo-excitation,
the novel "Type-3" IQHE in the high mobility specimen.Comment: 11 pages, 12 color figure
Electrically tunable GHz oscillations in doped GaAs-AlAs superlattices
Tunable oscillatory modes of electric-field domains in doped semiconductor
superlattices are reported. The experimental investigations demonstrate the
realization of tunable, GHz frequencies in GaAs-AlAs superlattices covering the
temperature region from 5 to 300 K. The orgin of the tunable oscillatory modes
is determined using an analytical and a numerical modeling of the dynamics of
domain formation. Three different oscillatory modes are found. Their presence
depends on the actual shape of the drift velocity curve, the doping density,
the boundary condition, and the length of the superlattice. For most bias
regions, the self-sustained oscillations are due to the formation, motion, and
recycling of the domain boundary inside the superlattice. For some biases, the
strengths of the low and high field domain change periodically in time with the
domain boundary being pinned within a few quantum wells. The dependency of the
frequency on the coupling leads to the prediction of a new type of tunable GHz
oscillator based on semiconductor superlattices.Comment: Tex file (20 pages) and 16 postscript figure
Characteristics of interface corrugations in short-period GaAs/AlAs superlattices
GaAs/AlAs supelattices with corrugated interfaces have been investigated by the polarized photoluminescence method. Using the theoretical approach, which associates the linear polarization of exciton photoluminescence with the corrugation parameters, experimental results have been fitted to determine the height and lateral extension of corrugations.Методом поляризованої фотолюмінесценції досліджені надгратки GaAs/AlAs з коругованими гетеромережами. Співставляючи експериментальні результати з теоретичними розрахунками на основі моделі, яка пов'язує ступінь лінійної поляризації екситонної фотолюмінесценції з параметрами коругованостей, визначені висота та латеральна протяжність коругованостей.Методом поляризованной фотолюминесценции исследованы сверхрешетки GaAs/AlAs с корругированными гетерограницами. Путем сравнения експериментальных результатов с теоретическими расчетами, базирующимися на модели, которая связывает степень линейной поляризации экситонной фотолюминесценции з параметрами корругованностей, определены высота и латеральная протяженность корругованностей
Collective coherence in planar semiconductor microcavities
Semiconductor microcavities, in which strong coupling of excitons to confined
photon modes leads to the formation of exciton-polariton modes, have
increasingly become a focus for the study of spontaneous coherence, lasing, and
condensation in solid state systems. This review discusses the significant
experimental progress to date, the phenomena associated with coherence which
have been observed, and also discusses in some detail the different theoretical
models that have been used to study such systems. We consider both the case of
non-resonant pumping, in which coherence may spontaneously arise, and the
related topics of resonant pumping, and the optical parametric oscillator.Comment: 46 pages, 12 figure
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