6,115 research outputs found
Improved chlorate candle provides concentrated oxygen source
Improved chlorate candle is used as a solid, portable source of oxygen in emergency situations. It contains sodium chlorate, iron, barium peroxide, and glass mixed in powdered form. The oxygen evolves from the decomposition of the sodium chlorate when an ignition pellet is electrically initiated
Spin noise spectroscopy in GaAs
We observe the noise spectrum of electron spins in bulk GaAs by Faraday
rotation noise spectroscopy. The experimental technique enables the undisturbed
measurement of the electron spin dynamics in semiconductors. We measure
exemplarily the electron spin relaxation time and the electron Lande g-factor
in n-doped GaAs at low temperatures and find good agreement of the measured
noise spectrum with an unpretentious theory based on Poisson distribution
probability.Comment: 4 pages, 4 figure
Parasitic pumping currents in an interacting quantum dot
We analyze the charge and spin pumping in an interacting dot within the
almost adiabatic limit. By using a non-equilibrium Green's function technique
within the time-dependent slave boson approximation, we analyze the pumped
current in terms of the dynamical constraints in the infinite-U regime. The
results show the presence of parasitic pumping currents due to the additional
phases of the constraints. The behavior of the pumped current through the
quantum dot is illustrated in the spin-insensitive and in the spin-sensitive
case relevant for spintronics applications
Competition between Kondo screening and quantum Hall edge reconstruction
We report on a Kondo correlated quantum dot connected to two-dimensional
leads where we demonstrate the renormalization of the g-factor in the pure
Zeeman case i.e, for magnetic fields parallel to the plane of the quantum dot.
For the same system we study the influence of orbital effects by investigating
the quantum Hall regime i.e. a perpendicular magnetic field is applied. In this
case an unusual behaviour of the suppression of the Kondo effect and of the
split zero-bias anomaly is observed. The splitting decreases with magnetic
field and shows discontinuous changes which are attributed to the intricate
interplay between Kondo screening and the quantum Hall edge structure
originating from electrostatic screening. This edge structure made up of
compressible and incompressible stripes strongly affects the Kondo temperature
of the quantum dot and thereby influences the renormalized g-factor
Probing a Kondo correlated quantum dot with spin spectroscopy
We investigate Kondo effect and spin blockade observed on a many-electron
quantum dot and study the magnetic field dependence. At lower fields a
pronounced Kondo effect is found which is replaced by spin blockade at higher
fields. In an intermediate regime both effects are visible. We make use of this
combined effect to gain information about the internal spin configuration of
our quantum dot. We find that the data cannot be explained assuming regular
filling of electronic orbitals. Instead spin polarized filling seems to be
probable.Comment: 4 pages, 5 figure
Quantitative validation of PEDFLOW for description of unidirectional pedestrian dynamics
The results of a systematic quantitative validation of PEDFLOW based on the
experimental data from FZJ are presented. Unidirectional flow experiments,
totaling 28 different combinations with varying entry, corridor and exit
widths, were considered. The condition imposed on PEDFLOW was that all the
cases should be run with the same input parameters. The exit times and
fundamental diagrams for the measuring region were evaluated and compared. This
validation process led to modifications and enhancements of the model
underlying PEDFLOW. The preliminary conclusions indicate that the results agree
well for densities smaller than 3 m-2 and a good agreement is observed even at
high densities for the corridors with bcor = 2.4 m, and bcor = 3.0 m. For
densities between 1 and 2 m-2 the specific flow and velocities are
underpredicted by PEDFLOW.Comment: 6 pages, 3 figures, 1 Table, conference PED201
Magnetoresistance Induced by Rare Strong Scatterers in a High Mobility 2DEG
We observe a strong negative magnetoresistance at non-quantizing magnetic
fields in a high-mobility two-dimensional electron gas (2DEG). This strong
negative magnetoresistance consists of a narrow peak around zero magnetic field
and a huge magnetoresistance at larger fields. The peak shows parabolic
magnetic field dependence and is attributed to the interplay of smooth disorder
and rare strong scatterers. We identify the rare strong scatterers as
macroscopic defects in the material and determine their density from the peak
curvature.Comment: 5 pages, 4 figure
Theoretical study of electronic transport through a small quantum dot with a magnetic impurity
We model a small quantum dot with a magnetic impurity by the Anderson
Hamiltonian with a supplementary exchange interaction term. The transport
calculations are performed by means of the Green functions within the equation
of motion scheme, in which two decoupling procedures are proposed, for high and
low temperatures, respectively. The paper focuses on the charge fluctuations
for such a system, aspect not addressed before, as well as on the Kondo
resonance. We show a specific role of the excited state, which can be observed
in transport and in spin-spin correlations. Our studies show on a new many-body
feature of the phase shift of transmitted electrons, which is manifested in a
specific dip. In the Kondo regime, our calculations complement existing
theoretical results. The system shows three Kondo peaks in the density of
states: one at the Fermi energy and two side peaks, at a distance corresponding
to the singlet-triplet level spacing. The existence of the central peak is
conditioned by a degenerate state (the triplet) below the Fermi energy.Comment: 12 pages, 4 figure
Polarons in semiconductor quantum-dots and their role in the quantum kinetics of carrier relaxation
While time-dependent perturbation theory shows inefficient carrier-phonon
scattering in semiconductor quantum dots, we demonstrate that a quantum kinetic
description of carrier-phonon interaction predicts fast carrier capture and
relaxation. The considered processes do not fulfill energy conservation in
terms of free-carrier energies because polar coupling of localized quantum-dot
states strongly modifies this picture.Comment: 6 pages, 6 figures, accepted for publication in Phys.Rev.
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