235 research outputs found
Nonlinear dynamics of polariton scattering in semiconductor microcavity: bistability vs stimulated scattering
We demonstrate experimentally an unusual behavior of the parametric polariton
scattering in semiconductor microcavity under a strong cw resonant excitation.
The maximum of the scattered signal above the threshold of stimulated
parametric scattering does not shift along the microcavity lower polariton
branch with the change of pump detuning or angle of incidence but is stuck
around the normal direction. We show theoretically that such a behavior can be
modelled numerically by a system of Maxwell and nonlinear Schroedinger
equations for cavity polaritons and explained via the competition between the
bistability of a driven nonlinear MC polariton and the instabilities of
parametric polariton-polariton scattering.Comment: 5 pages, 4 Postscript figures; corrected typo
Terahertz emitters based on microcavity dipolaritons
We propose the use of dipolaritons -- quantum well excitons with large dipole
moment, coupled to a planar microcavity -- for generating terahertz (THz)
radiation. This is achieved by exciting the system with two THz detuned lasers
that leads to dipole moment oscillations of the exciton polariton at the
detuning frequency, thus generating a THz emission. We have optimized the
structural parameters of a system with microcavity embedded AlGaAs double
quantum wells and shown that the THz emission intensity is maximized if the
laser frequencies both match different dipolariton states. The influence of the
electronic tunnel coupling between the wells on the frequency and intensity of
the THz radiation is also investigated, demonstrating a trade-off between the
polariton dipole moment and the Rabi splitting.Comment: 4 pages, 4 figures. This article has been submitted to Applied
Physics Letter
Size-dependence of anisotropic exchange interaction in InAs/GaAs quantum dots
A comprehensive study of the exchange interaction between charge carriers in
self-organized InAs/GaAs quantum dots is presented. Single quantum-dot
cathodoluminescence spectra of quantum dots of different sizes are analyzed.
Special attention is paid to the energetic structure of the charged excited
exciton (hot trion). A varying degree of intermixing within the hot trion
states leads to varying degrees of polarization of the corresponding emission
lines. The emission characteristics change from circularly polarized for small
quantum dots to elliptically polarized for large quantum dots. The findings are
explained by a change of magnitude of the anisotropic exchange interaction and
compared to the related effect of fine-structure splitting in the neutral
exciton and biexciton emission.Comment: 4 pages, 3 figures, to be published in phys. stat. sol (b),
proceedings of the QD2006, May 1-5 2006, Chamonix-Mont-Blanc, Franc
Spin multistability of cavity polaritons in a magnetic field
Spin transitions are studied theoretically and experimentally in a resonantly
excited system of cavity polaritons in a magnetic field. Weak pair interactions
in this boson system make possible fast and massive spin flips occurring at
critical amplitudes due to the interplay between amplitude dependent shifts of
eigenstates and the Zeeman splitting. Dominant spin of a condensate can be
toggled forth and back by tuning of the pump intensity only, which opens the
way for ultra-fast spin switchings of polariton condensates on a picosecond
timescale.Comment: 4 pages, 4 figure
Optical Orientation of Excitons in CdSe Self-Assembled Quantum Dots
We study spin dynamics of excitons confined in self-assembled CdSe quantum
dots by means of optical orientation in magnetic field. At zero field the
exciton emission from QDs populated via LO phonon-assisted absorption shows a
circular polarization of 14%. The polarization degree of the excitonic emission
increases dramatically when a magnetic field is applied. Using a simple model,
we extract the exciton spin relaxation times of 100 ps and 2.2 ns in the
absence and presence of magnetic field, respectively. With increasing
temperature the polarization of the QD emission gradually decreases.
Remarkably, the activation energy which describes this decay is independent of
the external magnetic field, and, therefore, of the degeneracy of the exciton
levels in QDs. This observation implies that the temperature-induced
enhancement of the exciton spin relaxation is insensitive to the energy level
degeneracy and can be attributed to the same excited state distribution.Comment: 21 pages, 7 figs - PDF format onl
Nonlinear emission dynamics of a GaAs microcavity with embedded quantum wells
The emission dynamics of a GaAs microcavity at different angles of
observation with respect to the sample normal under conditions of nonresonant
picosecond-pulse excitation is measured. At sufficiently high excitation
densities, the decay time of the lower-polariton emission increases with the
polariton wavevector; at low excitation densities the decay time is independent
of the wavevector. The effect of additional nonresonant continuous illumination
on the emission originating from the bottom of the lower polariton branch is
investigated. The additional illumination leads to a substantial increase in
the emission intensity (considerably larger than the intensity of the
photoluminescence excited by this illumination alone). This fact is explained
in terms of acceleration of the polariton relaxation to the radiative states
due to scattering by charge carriers created by the additional illumination.
The results obtained show, that at large negative detunings between the photon
and exciton modes, polariton-polariton and polariton-free carrier scattering
are the main processes responsible for the filling of states near the bottom of
the lower polariton branch.Comment: 10 pages, 6 figures. This is an author-created, un-copyedited version
of an article accepted for publication in Journal of Physics: Condesed
Matter. IOP Publishing Ltd is not responsible for any errors or omissions in
this version of the manuscript or any version derived from i
Kinetics of stimulated polariton scattering in planar microcavities: Evidence for a dynamically self-organized optical parametric oscillator
We demonstrate for the first time the strong temporal hysteresis effects in
the kinetics of the pumped and scattered polariton populations in a planar
semiconductor microcavity under a nano-second-long pulsed resonant (by
frequency and angle) excitation above the lower polariton branch. The
hysteresis effects are explained in the model of multi-mode scattering when the
bistability of the nonlinear pumped polariton is accompanied by the explosive
growth of the scattered polaritons population. Subsequent self-organization
process in the nonlinear polariton system results in a new -- dynamically
self-organized -- type of optical parametric oscillator.Comment: 4 pages, 4 figure
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