2,426 research outputs found
Dynamics of the triple contact line on a non-isothermal heater at partial wetting
The dynamics of the triple gas-liquid-solid contact line is analysed for the
case where the gas is the saturated vapour corresponding to the liquid, like in
the vapour bubble in boiling. It is shown that even small superheating (with
respect to the saturation temperature) causes evaporation of the adsorption
liquid film and the true triple contact is established. It is shown that the
hydrodynamic contact line singularity cannot be relaxed with the Navier slip
condition under such circumstances. Augmented with the second derivative slip
condition is proposed to be applied. For the partial wetting conditions, a
non-stationary contact line problem where the contact line motion is caused by
evaporation or condensation is treated in the lubrication approximation in the
vicinity of the contact line. High heat fluxes in this region require the
transient heat conduction inside the heater to be accounted for. Two 2D
problems, those of drop retraction with no phase change and of drop evaporation
are solved and analysed as illustrations of the proposed approach
Radiative cascade from quantum dot metastable spin-blockaded biexciton
We detect a novel radiative cascade from a neutral semiconductor quantum dot.
The cascade initiates from a metastable biexciton state in which the holes form
a spin-triplet configuration, Pauli-blockaded from relaxation to the
spin-singlet ground state. The triplet biexciton has two photon-phonon-photon
decay paths. Unlike in the singlet-ground state biexciton radiative cascade, in
which the two photons are co-linearly polarized, in the triplet biexciton
cascade they are crosslinearly polarized. We measured the two-photon
polarization density matrix and show that the phonon emitted when the
intermediate exciton relaxes from excited to ground state, preserves the
exciton's spin. The phonon, thus, does not carry with it any which-path
information other than its energy. Nevertheless, entanglement distillation by
spectral filtering was found to be rather ineffective for this cascade. This
deficiency results from the opposite sign of the anisotropic electron-hole
exchange interaction in the excited exciton relative to that in the ground
exciton.Comment: 6 pages, 4 figure
Spin injection in a single metallic nanoparticle: a step towards nanospintronics
We have fabricated nanometer sized magnetic tunnel junctions using a new
nanoindentation technique in order to study the transport properties of a
single metallic nanoparticle. Coulomb blockade effects show clear evidence for
single electron tunneling through a single 2.5 nm Au cluster. The observed
magnetoresistance is the signature of spin conservation during the transport
process through a non magnetic cluster.Comment: 3 page
Screening nuclear field fluctuations in quantum dots for indistinguishable photon generation
A semiconductor quantum dot can generate highly coherent and
indistinguishable single photons. However, intrinsic semiconductor dephasing
mechanisms can reduce the visibility of two-photon interference. For an
electron in a quantum dot, a fundamental dephasing process is the hyperfine
interaction with the nuclear spin bath. Here we directly probe the consequence
of the fluctuating nuclear spins on the elastic and inelastic scattered photon
spectra from a resident electron in a single dot. We find the nuclear spin
fluctuations lead to detuned Raman scattered photons which are distinguishable
from both the elastic and incoherent components of the resonance fluorescence.
This significantly reduces two-photon interference visibility. However, we
demonstrate successful screening of the nuclear spin noise which enables the
generation of coherent single photons that exhibit high visibility two-photon
interference.Comment: 5 pages, 4 figures + Supplementary Informatio
Externally mode-matched cavity quantum electrodynamics with charge-tunable quantum dots
We present coherent reflection spectroscopy on a charge and DC Stark tunable
quantum dot embedded in a high-quality and externally mode-matched microcavity.
The addition of an exciton to a single-electron charged quantum dot forms a
trion that interacts with the microcavity just below strong coupling regime of
cavity quantum electrodynamics. Such an integrated, monolithic system is a
crucial step towards the implementation of scalable hybrid quantum information
schemes that are based on an efficient interaction between a single photon and
a confined electron spin.Comment: 10 pages, 4 figure
Polarization sensitive spectroscopy of charged Quantum Dots
We present an experimental and theoretical study of the polarized
photoluminescence spectrum of single semiconductor quantum dots in various
charge states. We compare our high resolution polarization sensitive spectral
measurements with a new many-carrier theoretical model, which was developed for
this purpose. The model considers both the isotropic and anisotropic exchange
interactions between all participating electron-hole pairs. With this addition,
we calculate both the energies and polarizations of all optical transitions
between collective, quantum dot confined charge carrier states. We succeed in
identifying most of the measured spectral lines. In particular, the lines
resulting from singly-, doubly- and triply- negatively charged excitons and
biexcitons. We demonstrate that lines emanating from evenly charged states are
linearly polarized. Their polarization direction does not necessarily coincide
with the traditional crystallographic direction. It depends on the shells of
the single carriers, which participate in the recombination process.Comment: 11 pages, 9 figures. Revised versio
Dislocation Free Island Formation in Heteroepitaxial Growth: An Equilibrium Study
We investigate the equilibrium properties of strained heteroepitaxial
systems, incorporating the formation and the growth of a wetting film,
dislocation free island formation, and ripening. The derived phase diagram
provides a detailed characterization of the possible growth modes in terms of
the island density, equilibrium island size, and wetting layer thickness.
Comparing our predictions with experimental results we discuss the growth
conditions that can lead to stable islands as well as ripening.Comment: 4 pages, LaTeX, 3 ps figure
Electro-elastic tuning of single particles in individual self-assembled quantum dots
We investigate the effect of uniaxial stress on InGaAs quantum dots in a
charge tunable device. Using Coulomb blockade and photoluminescence, we observe
that significant tuning of single particle energies (~ -0.5 meV/MPa) leads to
variable tuning of exciton energies (+18 to -0.9 micro-eV/MPa) under tensile
stress. Modest tuning of the permanent dipole, Coulomb interaction and
fine-structure splitting energies is also measured. We exploit the variable
exciton response to tune multiple quantum dots on the same chip into resonance.Comment: 16 pages, 4 figures, 1 table. Final versio
Metal-Insulator Transition in a Disordered Two-Dimensional Electron Gas in GaAs-AlGaAs at zero Magnetic Field
A metal-insulator transition in two-dimensional electron gases at B=0 is
found in Ga(Al)As heterostructures, where a high density of self-assembled InAs
quantum dots is incorporated just 3 nm below the heterointerface. The
transition occurs at resistances around h/e^2 and critical carrier densities of
1.2 10^11cm^-2. Effects of electron-electron interactions are expected to be
rather weak in our samples, while disorder plays a crucial role.Comment: 4 pages, 3 figures, 21 reference
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