1,544 research outputs found
Single exciton spectroscopy of single-Mn doped InAs quantum dots
The optical spectroscopy of a single InAs quantum dot doped with a single Mn
atom is studied using a model Hamiltonian that includes the exchange
interactions between the spins of the quantum dot electron-hole pair, the Mn
atom and the acceptor hole. Our model permits to link the photoluminescence
spectra to the Mn spin states after photon emission. We focus on the relation
between the charge state of the Mn, or , and the different spectra
which result through either band-to-band or band-to-acceptor transitions. We
consider both neutral and negatively charged dots. Our model is able to account
for recent experimental results on single Mn doped InAs PL spectra and can be
used to account for future experiments in GaAs quantum dots. Similarities and
differences with the case of single Mn doped CdTe quantum dots are discussed.Comment: 15 pages, 9 figure
Geometric and compositional influences on spin-orbit induced circulating currents in nanostructures
Circulating orbital currents, originating from the spin-orbit interaction,
are calculated for semiconductor nanostructures in the shape of spheres, disks,
spherical shells and rings for the electron ground state with spin oriented
along a symmetry axis. The currents and resulting orbital and spin magnetic
moments, which combine to yield the effective electron g factor, are calculated
using a recently introduced formalism that allows the relative contributions of
different regions of the nanostructure to be identified. For all these
spherically or cylindrically symmetric hollow or solid nanostructures,
independent of material composition and whether the boundary conditions are
hard or soft, the dominant orbital current originates from intermixing of
valence band states in the electron ground state, circulates within the
nanostructure, and peaks approximately halfway between the center and edge of
the nanostructure in the plane perpendicular to the spin orientation. For a
specific material composition and confinement character, the confinement energy
and orbital moment are determined by a single size-dependent parameter for
spherically symmetrical nanostructures, whereas they can be independently tuned
for cylindrically symmetric nanostructures.Comment: 22 pages, 20 figure
Spin-orbit-induced circulating currents in a semiconductor nanostructure
Circulating orbital currents produced by the spin-orbit interaction for a
single electron spin in a quantum dot are explicitly evaluated at zero magnetic
field, along with their effect on the total magnetic moment (spin and orbital)
of the electron spin. The currents are dominated by coherent superpositions of
the conduction and valence envelope functions of the electronic state, are
smoothly varying within the quantum dot, and are peaked roughly halfway between
the dot center and edge. Thus the spatial structure of the spin contribution to
the magnetic moment (which is peaked at the dot center) differs greatly from
the spatial structure of the orbital contribution. Even when the spin and
orbital magnetic moments cancel (for ) the spin can interact strongly with
local magnetic fields, e.g. from other spins, which has implications for spin
lifetimes and spin manipulation.Comment: 6 pages, 3 figure
Subchondral bone density distribution of the talus in clinically normal Labrador Retrievers
Background: Bones continually adapt their morphology to their load bearing function. At the level of the subchondral bone, the density distribution is highly correlated with the loading distribution of the joint. Therefore, subchondral bone density distribution can be used to study joint biomechanics non-invasively. In addition physiological and pathological joint loading is an important aspect of orthopaedic disease, and research focusing on joint biomechanics will benefit veterinary orthopaedics. This study was conducted to evaluate density distribution in the subchondral bone of the canine talus, as a parameter reflecting the long-term joint loading in the tarsocrural joint.
Results: Two main density maxima were found, one proximally on the medial trochlear ridge and one distally on the lateral trochlear ridge. All joints showed very similar density distribution patterns and no significant differences were found in the localisation of the density maxima between left and right limbs and between dogs.
Conclusions: Based on the density distribution the lateral trochlear ridge is most likely subjected to highest loads within the tarsocrural joint. The joint loading distribution is very similar between dogs of the same breed. In addition, the joint loading distribution supports previous suggestions of the important role of biomechanics in the development of OC lesions in the tarsus. Important benefits of computed tomographic osteoabsorptiometry (CTOAM), i.e. the possibility of in vivo imaging and temporal evaluation, make this technique a valuable addition to the field of veterinary orthopaedic research
g-Factors and diamagnetic coefficients of electrons, holes and excitons in InAs/InP quantum dots
The electron, hole, and exciton g-factors and diamagnetic coefficients have
been calculated using envelope-function theory for cylindrical InAs/InP quantum
dots in the presence of a magnetic field parallel to the dot symmetry axis. A
clear connection is established between the electron g-factor and the amplitude
of the those valence-state envelope functions which possess non-zero orbital
momentum associated with the envelope function. The dependence of the exciton
diamagnetic coefficients on the quantum dot height is found to correlate with
the energy dependence of the effective mass. Calculated exciton g-factor and
diamagnetic coefficients, constructed from the values associated with the
electron and hole constituents of the exciton, match experimental data well,
however including the Coulomb interaction between the electron and hole states
improves the agreement. Remote-band contributions to the valence-band
electronic structure, included perturbatively, reduce the agreement between
theory and experiment.Comment: 12 pages, 7 figure
Size dependent exciton g-factor in self-assembled InAs/InP quantum dots
We have studied the size dependence of the exciton g-factor in self-assembled
InAs/InP quantum dots. Photoluminescence measurements on a large ensemble of
these dots indicate a multimodal height distribution. Cross-sectional Scanning
Tunneling Microscopy measurements have been performed and support the
interpretation of the macro photoluminescence spectra. More than 160 individual
quantum dots have systematically been investigated by analyzing single dot
magneto-luminescence between 1200nm and 1600 nm. We demonstrate a strong
dependence of the exciton g-factor on the height and diameter of the quantum
dots, which eventually gives rise to a sign change of the g-factor. The
observed correlation between exciton g-factor and the size of the dots is in
good agreement with calculations. Moreover, we find a size dependent anisotropy
splitting of the exciton emission in zero magnetic field.Comment: 15 pages, 7 figure
Overruled!: Implicit cues rather than an orthographic rule determine Dutch children's vowel spelling
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