109 research outputs found
Temperature dependence of exciton recombination in semiconducting single-wall carbon nanotubes
We study the excitonic recombination dynamics in an ensemble of (9,4)
semiconducting single-wall carbon nanotubes by high sensitivity time-resolved
photo-luminescence experiments. Measurements from cryogenic to room temperature
allow us to identify two main contributions to the recombination dynamics. The
initial fast decay is temperature independent and is attributed to the presence
of small residual bundles that create external non-radiative relaxation
channels. The slow component shows a strong temperature dependence and is
dominated by non-radiative processes down to 40 K. We propose a quantitative
phenomenological modeling of the variations of the integrated photoluminescence
intensity over the whole temperature range. We show that the luminescence
properties of carbon nanotubes at room temperature are not affected by the
dark/bright excitonic state coupling
Excitation transfer and luminescence in porphyrin-carbon nanotube complexes
Functionalization of carbon nanotubes with hydrosoluble porphyrins (TPPS) is
achieved by "-stacking". The porphyrin/nanotube interaction is studied by
means of optical absorption, photoluminescence and photoluminescence excitation
spectroscopies. The main absorption line of the porphyrins adsorbed on
nanotubes exhibits a 120 meV red shift, which we ascribe to a flattening of the
molecule in order to optimize interactions. The porphyrin-nanotube
complex shows a strong quenching of the TPPS emission while the
photoluminescence intensity of the nanotubes is enhanced when the excitation
laser is in resonance with the porphyrin absorption band. This reveals an
efficient excitation transfer from the TPPS to the carbon nanotube
Time-resolved spectroscopy of multi-excitonic decay in an InAs quantum dot
The multi-excitonic decay process in a single InAs quantum dot is studied
through high-resolution time-resolved spectroscopy. A cascaded emission
sequence involving three spectral lines is seen that is described well over a
wide range of pump powers by a simple model. The measured biexcitonic decay
rate is about 1.5 times the single-exciton decay rate. This ratio suggests the
presence of selection rules, as well as a significant effect of the Coulomb
interaction on the biexcitonic wavefunction.Comment: one typo fixe
Unconventional motional narrowing in the optical spectrum of a semiconductor quantum dot
Motional narrowing refers to the striking phenomenon where the resonance line
of a system coupled to a reservoir becomes narrower when increasing the
reservoir fluctuation. A textbook example is found in nuclear magnetic
resonance, where the fluctuating local magnetic fields created by randomly
oriented nuclear spins are averaged when the motion of the nuclei is thermally
activated. The existence of a motional narrowing effect in the optical response
of semiconductor quantum dots remains so far unexplored. This effect may be
important in this instance since the decoherence dynamics is a central issue
for the implementation of quantum information processing based on quantum dots.
Here we report on the experimental evidence of motional narrowing in the
optical spectrum of a semiconductor quantum dot broadened by the spectral
diffusion phenomenon. Surprisingly, motional narrowing is achieved when
decreasing incident power or temperature, in contrast with the standard
phenomenology observed for nuclear magnetic resonance
Bistable Helmholtz bright solitons in saturable materials
We present, to the best of our knowledge, the first exact analytical solitons of a nonlinear Helmholtz equation with a saturable refractive-index model. These new two-dimensional spatial solitons have a bistable characteristic in some parameter regimes, and they capture oblique (arbitrary-angle) beam propagation in both the forward and backward directions. New conservation laws are reported, and the classic paraxial solution is recovered in an appropriate multiple limit. Analysis and simulations examine the stability of both solution branches, and stationary Helmholtz solitons are found to emerge from a range of perturbed input beams
Center-of-Mass Properties of the Exciton in Quantum Wells
We present high-quality numerical calculations of the exciton center-of-mass
dispersion for GaAs/AlGaAs quantum wells of widths in the range 2-20 nm. The
k.p-coupling of the heavy- and light-hole bands is fully taken into account. An
optimized center-of-mass transformation enhances numerical convergence. We
derive an easy-to-use semi-analytical expression for the exciton groundstate
mass from an ansatz for the exciton wavefunction at finite momentum. It is
checked against the numerical results and found to give very good results. We
also show multiband calculations of the exciton groundstate dispersion using a
finite-differences scheme in real space, which can be applied to rather general
heterostructures.Comment: 19 pages, 12 figures included, to be published in Phys. Rev.
Exciton Spin Dynamics in Semiconductor Quantum Wells
In this paper we will review Exciton Spin Dynamics in Semiconductor Quantum
Wells. The spin properties of excitons in nanostructures are determined by
their fine structure. We will mainly focus in this review on GaAs and InGaAs
quantum wells which are model systems.Comment: 55 pages, 27 figure
Mutations in the gene encoding the synaptic scaffolding protein SHANK3 are associated with autism spectrum disorders.
International audienceSHANK3 (also known as ProSAP2) regulates the structural organization of dendritic spines and is a binding partner of neuroligins; genes encoding neuroligins are mutated in autism and Asperger syndrome. Here, we report that a mutation of a single copy of SHANK3 on chromosome 22q13 can result in language and/or social communication disorders. These mutations concern only a small number of individuals, but they shed light on one gene dosage-sensitive synaptic pathway that is involved in autism spectrum disorders
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