1,178 research outputs found
Photoluminescence and spectral switching of single CdSe/ZnS colloidal nanocrystals in poly(methyl methacrylate)
Emission from single CdSe nanocrystals in PMMA was investigated. A fraction
of the nanocrystals exhibiting switching between two energy states, which have
similar total intensities, but distinctly different spectra were observed. We
found that the spectral shift characteristic frequency increases with the pump
power. By using the dynamic shift in the spectral position of emission peaks,
we were able to correlate peaks from the same nanocrystal. The measured
correlation is consistent with assignment of low energy lines to phonon
replicas.Comment: 5 pages, 4 figure
Eigenvalue spectrum for single particle in a spheroidal cavity: A Semiclassical approach
Following the semiclassical formalism of Strutinsky et al., we have obtained
the complete eigenvalue spectrum for a particle enclosed in an infinitely high
spheroidal cavity. Our spheroidal trace formula also reproduces the results of
a spherical billiard in the limit . Inclusion of repetition of each
family of the orbits with reference to the largest one significantly improves
the eigenvalues of sphere and an exact comparison with the quantum mechanical
results is observed upto the second decimal place for . The
contributions of the equatorial, the planar (in the axis of symmetry plane) and
the non-planar(3-Dimensional) orbits are obtained from the same trace formula
by using the appropriate conditions. The resulting eigenvalues compare very
well with the quantum mechanical eigenvalues at normal deformation. It is
interesting that the partial sum of equatorial orbits leads to eigenvalues with
maximum angular momentum projection, while the summing of planar orbits leads
to eigenvalues with except for L=1. The remaining quantum mechanical
eigenvalues are observed to arise from the 3-dimensional(3D) orbits. Very few
spurious eigenvalues arise in these partial sums. This result establishes the
important role of 3D orbits even at normal deformations.Comment: 17 pages, 7 ps figure
Optically-controlled single-qubit rotations in self-assembled InAs quantum dots
We present a theory of the optical control of the spin of an electron in an
InAs quantum dot. We show how two Raman-detuned laser pulses can be used to
obtain arbitrary single-qubit rotations via the excitation of an intermediate
trion state. Our theory takes into account a finite in-plane hole -factor
and hole-mixing. We show that such rotations can be performed to high
fidelities with pulses lasting a few tens of picoseconds.Comment: 6 pages, 4 figures; minor changes, J-ref adde
Indirect coupling between spins in semiconductor quantum dots
The optically induced indirect exchange interaction between spins in two
quantum dots is investigated theoretically. We present a microscopic
formulation of the interaction between the localized spin and the itinerant
carriers including the effects of correlation, using a set of canonical
transformations. Correlation effects are found to be of comparable magnitude as
the direct exchange. We give quantitative results for realistic quantum dot
geometries and find the largest couplings for one dimensional systems.Comment: 4 pages, 3 figure
Sonic hedgehog regulates the proliferation, differentiation, and migration of enteric neural crest cells in gut
Enteric neural crest cells (NCCs) migrate and colonize the entire gut and proliferate and differentiate into neurons and glia of the enteric nervous system in vertebrate embryos. We have investigated the mitogenic and morphogenic functions of Sonic hedgehog (Shh) on enteric NCCs in cell and organ culture. Enteric NCCs expressed Shh receptor Patched and transcripts encoding the Shh signal transducer (Gli1). Shh promoted the proliferation and inhibited the differentiation of NCCs. The pro-neurogenic effect of glial cell line-derived neurotrophic factor (GDNF) on NCCs was abolished by Shh. In gut explants, NCCs migrated from the explants onto the adjacent substratum if GDNF was added, whereas addition of Shh abolished this migration. Neuronal differentiation and coalescence of neural crest-derived cells into myenteric plexuses in explants was repressed by the addition of Shh. Our data suggest that Shh controls the proliferation and differentiation of NCCs and modulates the responsiveness of NCCs toward GDNF inductions.published_or_final_versio
Mapping loci influencing blood pressure in the Framingham pedigrees using model-free LOD score analysis of a quantitative trait
This paper presents a method of performing model-free LOD-score based linkage analysis on quantitative traits. It is implemented in the QMFLINK program. The method is used to perform a genome screen on the Framingham Heart Study data. A number of markers that show some support for linkage in our study coincide substantially with those implicated in other linkage studies of hypertension. Although the new method needs further testing on additional real and simulated data sets we can already say that it is straightforward to apply and may offer a useful complementary approach to previously available methods for the linkage analysis of quantitative traits
Many-body diagrammatic expansion in a Kohn-Sham basis: implications for Time-Dependent Density Functional Theory of excited states
We formulate diagrammatic rules for many-body perturbation theory which uses
Kohn-Sham (KS) Green's functions as basic propagators. The diagram technique
allows to study the properties of the dynamic nonlocal exchange-correlation
(xc) kernel . We show that the spatial non-locality of is
strongly frequency-dependent. In particular, in extended systems the
non-locality range diverges at the excitation energies. This divergency is
related to the discontinuity of the xc potential.Comment: 4 RevTeX pages including 3 eps figures, submitted to Phys. Rev. Lett;
revised version with new reference
Ultrafast demagnetization in the sp-d model: a theoretical study
We propose and analyze a theoretical model of ultrafast light-induced
magnetization dynamics in systems of localized spins that are coupled to
carriers' spins by sp-d exchange interaction. A prominent example of a class of
materials falling into this category are ferromagnetic (III,Mn)V
semiconductors, in which ultrafast demagnetization has been recently observed.
In the proposed model light excitation heats up the population of carriers,
taking it out of equilibrium with the localized spins. This triggers the
process of energy and angular momentum exchange between the two spin systems,
which lasts for the duration of the energy relaxation of the carriers. We
derive the Master equation for the density matrix of a localized spin
interacting with the hot carriers and couple it with a phenomenological
treatment of the carrier dynamics. We develop a general theory within the sp-d
model and we apply it to the ferromagnetic semiconductors, taking into account
the valence band structure of these materials. We show that the fast spin
relaxation of the carriers can sustain the flow of polarization between the
localized and itinerant spins leading to significant demagnetization of the
localized spin system, observed in (III,Mn)V materials.Comment: 15 pages, 8 figure
Kondo Insulator: p-wave Bose Condensate of Excitons
In the Anderson lattice model for a mixed-valent system, the
hybridization can possess a -wave symmetry. The strongly-correlated
insulating phase in the mean-field approximation is shown to be a -wave Bose
condensate of excitons with a spontaneous lattice deformation. We study the
equilibrium and linear response properties across the insulator-metal
transition. Our theory supports the empirical correlation between the lattice
deformation and the magnetic susceptibility and predicts measurable ultrasonic
and high-frequency phonon behavior in mixed-valent semiconductors.Comment: 5 pages, 3 encapsulated PostScript figure
Coherent transport in homojunction between excitonic insulator and semimetal
From the solution of a two-band model, we predict that the thermal and
electrical transport across the junction of a semimetal and an excitonic
insulator will exhibit high resistance behavior and low entropy production at
low temperatures, distinct from a junction of a semimetal and a normal
semiconductor. This phenomenon, ascribed to the dissipationless exciton flow
which dominates over the charge transport, is based on the much longer length
scale of the change of the effective interface potential for electron
scattering due to the coherence of the condensate than in the normal state.Comment: RevTeX 4.0, 13 pages, 5 b/w figures, 1 colour figure, 1 table.
Version modified with respect to the original, which will appear in Physical
Review Letters. This version includes the supplementary (EPAPS) material as
an Appendix, and it is slightly longer than the accepted version (more text
and references
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