6,006 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
Channel Blockade in a Two-Path Triple-Quantum-Dot System
Electronic transport through a two-path triple-quantum-dot system with two
source leads and one drain is studied. By separating the conductance of the two
double dot paths, we are able to observe double dot and triple dot physics in
transport and study the interaction between the paths. We observe channel
blockade as a result of inter-channel Coulomb interaction. The experimental
results are understood with the help of a theoretical model which calculates
the parameters of the system, the stability regions of each state and the full
dynamical transport in the triple dot resonances.Comment: 6 pages, 6 figure
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
Giant anisotropy of Zeeman splitting of quantum confined acceptors in Si/Ge
Shallow acceptor levels in Si/Ge/Si quantum well heterostructures are
characterized by resonant tunneling spectroscopy in the presence of high
magnetic fields. In a perpendicular magnetic field we observe a linear Zeeman
splitting of the acceptor levels. In an in-plane field, on the other hand, the
Zeeman splitting is strongly suppressed. This anisotropic Zeeman splitting is
shown to be a consequence of the huge light hole-heavy hole splitting caused by
a large biaxial strain and a strong quantum confinement in the Ge quantum well.Comment: 5 figures, 4 page
Noise enhancement due to quantum coherence in coupled quantum dots
We show that the intriguing observation of noise enhancement in the charge
transport through two vertically coupled quantum dots can be explained by the
interplay of quantum coherence and strong Coulomb blockade. We demonstrate that
this novel mechanism for super-Poissonian charge transfer is very sensitive to
decoherence caused by electron-phonon scattering as inferred from the measured
temperature dependence.Comment: 4 pages, 3 figures, corrected version (Figs.2 and 3
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.
Two path transport measurements on a triple quantum dot
We present an advanced lateral triple quantum dot made by local anodic
oxidation. Three dots are coupled in a starlike geometry with one lead attached
to each dot thus allowing for multiple path transport measurements with two
dots per path. In addition charge detection is implemented using a quantum
point contact. Both in charge measurements as well as in transport we observe
clear signatures of states from each dot. Resonances of two dots can be
established allowing for serial transport via the corresponding path. Quadruple
points with all three dots in resonance are prepared for different electron
numbers and analyzed concerning the interplay of the simultaneously measured
transport along both paths.Comment: 4 pages, 4 figure
Contact Atomic Structure and Electron Transport Through Molecules
Using benzene sandwiched between two Au leads as a model system, we
investigate from first principles the change in molecular conductance caused by
different atomic structures around the metal-molecule contact. Our motivation
is the variable situations that may arise in break junction experiments; our
approach is a combined density functional theory and Green function technique.
We focus on effects caused by (1) the presence of an additional Au atom at the
contact and (2) possible changes in the molecule-lead separation. The effects
of contact atomic relaxation and two different lead orientations are fully
considered. We find that the presence of an additional Au atom at each of the
two contacts will increase the equilibrium conductance by up to two orders of
magnitude regardless of either the lead orientation or different group-VI
anchoring atoms. This is due to a LUMO-like resonance peak near the Fermi
energy. In the non-equilibrium properties, the resonance peak manifests itself
in a large negative differential conductance. We find that the dependence of
the equilibrium conductance on the molecule-lead separation can be quite
subtle: either very weak or very strong depending on the separation regime.Comment: 8 pages, 6 figure
Ultrafast Magnetization Dynamics in Diluted Magnetic Semiconductors
We present a dynamical model that successfully explains the observed time
evolution of the magnetization in diluted magnetic semiconductor quantum wells
after weak laser excitation. Based on the pseudo-fermion formalism and a second
order many-particle expansion of the exact p-d exchange interaction, our
approach goes beyond the usual mean-field approximation. It includes both the
sub-picosecond demagnetization dynamics and the slower relaxation processes
which restore the initial ferromagnetic order in a nanosecond time scale. In
agreement with experimental results, our numerical simulations show that,
depending on the value of the initial lattice temperature, a subsequent
enhancement of the total magnetization may be observed within a time scale of
few hundreds of picoseconds.Comment: Submitted to PR
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