1,011 research outputs found
Single-dot Spectroscopy of GaAs Quantum Dots Fabricated by Filling of Self-assembled Nanoholes
We study the optical emission of single GaAs quantum dots (QDs). The QDs are fabricated by filling of nanoholes in AlGaAs and AlAs which are generated in a self-assembled fashion by local droplet etching with Al droplets. Using suitable process parameters, we create either uniform QDs in partially filled deep holes or QDs with very broad size distribution in completely filled shallow holes. Micro photoluminescence measurements of single QDs of both types establish sharp excitonic peaks. We measure a fine-structure splitting in the range of 22â40ÎŒeV and no dependence on QD size. Furthermore, we find a decrease in excitonâbiexciton splitting with increasing QD size
Quantized Dispersion of Two-Dimensional Magnetoplasmons Detected by Photoconductivity Spectroscopy
We find that the long-wavelength magnetoplasmon, resistively detected by
photoconductivity spectroscopy in high-mobility two-dimensional electron
systems, deviates from its well-known semiclassical nature as uncovered in
conventional absorption experiments. A clear filling-factor dependent
plateau-type dispersion is observed that reveals a so far unknown relation
between the magnetoplasmon and the quantum Hall effect.Comment: 5 pages, 3 figure
Kinetic estimate of the shielding of resonant magnetic field perturbations by the plasma in DIII-D
Kinetic modelling of bifurcation conditions of resonant magnetic perturbations in ASDEX Upgrade experiments
Strike point splitting induced by the application of magnetic perturbations on MAST
Divertor strike point splitting induced by resonant magnetic perturbations
(RMPs) has been observed on MAST for a variety of RMP configurations in a
plasma scenario with Ip=750kA where those configurations all have similar
resonant components. Complementary measurements have been obtained with
divertor Langmuir probes and an infrared camera. Clear splitting consistently
appears in this scenario only in the even configuration of the perturbation
coils, similarly to the density pump-out. These results present a challenge for
models of plasma response to RMPs.Comment: 9 pages, 4 figures, submitted to the proceedings of the 20th
Conference on Plasma Surface Interactions, to be published in the Journal of
Nuclear Material
Vector meson dominance and the rho meson
We discuss the properties of vector mesons, in particular the rho^0, in the
context of the Hidden Local Symmetry (HLS) model. This provides a unified
framework to study several aspects of the low energy QCD sector. Firstly, we
show that in the HLS model the physical photon is massless, without requiring
off field diagonalization. We then demonstrate the equivalence of HLS and the
two existing representations of vector meson dominance, VMD1 and VMD2, at both
tree level and one loop order. Finally the S matrix pole position is shown to
provide a model and process independent means of specifying the rho mass and
width, in contrast to the real axis prescription currently used in the Particle
Data Group tables.Comment: 18 pages, REVTE
Rho-Omega Mixing and the Pion Form Factor in the Time-like Region
We determine the magnitude, phase, and -dependence of -
``mixing'' in the pion form factor in the time-like region through fits to
e^+e^- \ra \pi^+ \pi^- data. The associated systematic errors in these
quantities, arising from the functional form used to fit the resonance,
are small. The systematic errors in the mass and width, however, are
larger than previously estimated.Comment: 20 pages, REVTeX, epsfig, 2 ps figures, minor change
Thermopower of a 2D electron gas in suspended AlGaAs/GaAs heterostructures
We present thermopower measurements on a high electron mobility
two-dimensional electron gas (2DEG) in a thin suspended membrane.We show that
the small dimension of the membrane substantially reduces the thermal
conductivity compared to bulk material so that it is possible to establish a
strong thermal gradient along the 2DEG even at a distance of few micrometers.
We find that the zero-field thermopower is significantly affected by the micro
patterning. In contrast to 2DEGs incorporated in a bulk material, the diffusion
contribution to the thermopower stays dominant up to a temperature of 7 K until
the phonon-drag becomes strong and governs the run of the thermopower. We also
find that the coupling between electrons and phonons in the phonon-drag regime
is due to screened deformation potentials, in contrast to piezoelectric
coupling found with bulk phonons.Comment: 7 page
- âŠ