1,868 research outputs found
Size-dependent fine-structure splitting in self-organized InAs/GaAs quantum dots
A systematic variation of the exciton fine-structure splitting with quantum
dot size in single InAs/GaAs quantum dots grown by metal-organic chemical vapor
deposition is observed. The splitting increases from -80 to as much as 520
eV with quantum dot size. A change of sign is reported for small quantum
dots. Model calculations within the framework of eight-band k.p theory and the
configuration interaction method were performed. Different sources for the
fine-structure splitting are discussed, and piezoelectricity is pinpointed as
the only effect reproducing the observed trend.Comment: 5 pages, 5 figure
Accretion of a satellite onto a spherical galaxy. II. Binary evolution and orbital decay
We study the dynamical evolution of a satellite orbiting outside of a
companion spherical galaxy. The satellite is subject to a back-reaction force
resulting from the density fluctuations excited in the primary stellar system.
We evaluate this force using the linear response theory developed in Colpi and
Pallavicini (1997). The force is computed in the reference frame comoving with
the primary galaxy and is expanded in multipoles. To capture the relevant
features of the physical process determining the evolution of the detached
binary, we introduce in the Hamiltonian the harmonic potential as interaction
potential among stars. The dynamics of the satellite is computed
self-consistently. We determine the conditions for tidal capture of a satellite
from an asymptotic free state. If the binary comes to existence as a bound
pair, stability against orbital decay is lost near resonance. The time scale of
binary coalescence is computed as a function of the eccentricity and mass
ratio. In a comparison with Weinberg's perturbative technique we demonstrate
that pinning the center of mass of the galaxy would induce a much larger torque
on the satellite.Comment: 13 pages, Tex,+ 10 .ps figures Submitted to The Astrophysical Journa
Multi-excitonic complexes in single InGaN quantum dots
Cathodoluminescence spectra employing a shadow mask technique of InGaN layers
grown by metal organic chemical vapor deposition on Si(111) substrates are
reported. Sharp lines originating from InGaN quantum dots are observed.
Temperature dependent measurements reveal thermally induced carrier
redistribution between the quantum dots. Spectral diffusion is observed and was
used as a tool to correlate up to three lines that originate from the same
quantum dot. Variation of excitation density leads to identification of exciton
and biexciton. Binding and anti-binding complexes are discovered.Comment: 3 pages, 4 figure
GaN/AlN Quantum Dots for Single Qubit Emitters
We study theoretically the electronic properties of -plane GaN/AlN quantum
dots (QDs) with focus on their potential as sources of single polarized photons
for future quantum communication systems. Within the framework of eight-band
k.p theory we calculate the optical interband transitions of the QDs and their
polarization properties. We show that an anisotropy of the QD confinement
potential in the basal plane (e.g. QD elongation or strain anisotropy) leads to
a pronounced linear polarization of the ground state and excited state
transitions. An externally applied uniaxial stress can be used to either induce
a linear polarization of the ground-state transition for emission of single
polarized photons or even to compensate the polarization induced by the
structural elongation.Comment: 6 pages, 9 figures. Accepted at Journal of Physics: Condensed Matte
Tidal Effects in Clusters of Galaxies
High-redshift clusters of galaxies show an over-abundance of spirals by a
factor of 2-3, and the corresponding under-abundance of S0 galaxies, relative
to the nearby clusters. This morphological evolution can be explained by tidal
interactions with neighboring galaxies and with the hierarchically growing
cluster halo. The efficiency of tidal interactions depends on the size and
structure of the cluster, as well as on the epoch of its formation. I simulate
the formation and evolution of Virgo-type clusters in three cosmologies: a
critical density model Omega_0=1, an open model Omega_0=0.4, and a flat model
Omega_0=0.4 with a cosmological constant. The orbits of identified halos are
traced with a high temporal resolution (~10^7 yr). Halos with low relative
velocities merge only shortly after entering the cluster; after virialization
mergers are suppressed. The dynamical evolution of galaxies is determined by
the tidal field along their trajectories. The maxima of the tidal force do not
always correspond to closest approach to the cluster center. They are produced
to a large extent by the local density structures, such as the massive galaxies
and the unvirialized remnants of infalling groups of galaxies. Collisions of
galaxies are intensified by the substructure, with about 10 encounters within
10 kpc per galaxy in the Hubble time. These very close encounters add an
important amount (10-50%) of the total heating rate. The integrated effect of
tidal interactions is insufficient to transform a spiral galaxy into an
elliptical, but can produce an S0 galaxy. Overall, tidal heating is stronger in
the low Omega_0 clusters
The Value of Liquidity
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72848/1/1080-8620.00026.pd
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