210 research outputs found
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
Quantum Interference Controls the Electron Spin Dynamics in n-GaAs
Manifestations of quantum interference effects in macroscopic objects are
rare. Weak localization is one of the few examples of such effects showing up
in the electron transport through solid state. Here we show that weak
localization becomes prominent also in optical spectroscopy via detection of
the electron spin dynamics. In particular, we find that weak localization
controls the free electron spin relaxation in semiconductors at low
temperatures and weak magnetic fields by slowing it down by almost a factor of
two in -doped GaAs in the metallic phase. The weak localization effect on
the spin relaxation is suppressed by moderate magnetic fields of about 1 T,
which destroy the interference of electron trajectories, and by increasing the
temperature. The weak localization suppression causes an anomalous decrease of
the longitudinal electron spin relaxation time with magnetic field, in
stark contrast with well-known magnetic field induced increase in . This
is consistent with transport measurements which show the same variation of
resistivity with magnetic field. Our discovery opens a vast playground to
explore quantum magneto-transport effects optically in the spin dynamics.Comment: 8 pages, 3 figure
Hierarchy and stability of partially synchronous oscillations of diffusively coupled dynamical systems
The paper presents a qualitative analysis of an array of diffusively coupled identical continuous time dynamical systems.The effects of full, partial, anti-phase and in-phase-anti-phase chaotic synchronization are investigated via the linear invariant manifolds of the corresponding differential equations. Existence of various invariant manifolds, a self-similar behavior, a hierarchy and embedding of the manifolds of the coupled system are discovered. Sufficient conditions for the stability of the invariant manifolds are obtained via the method of Lyapunov functions. Conditions under which full global synchronization can not be achieved even for the largest coupling constant are defined. The general rigorous results are illustrated through examples of coupled Lorenz-like and coupled Rössler systems
Cluster synchronization in three-dimensional lattices of diffusively coupled oscillators
Cluster synchronization modes of continuous time oscillators that are diffusively coupled in a three-dimensional (3-D) lattice are studied in the paper via the corresponding linear invariant manifolds. Depending in an essential way on the number of oscillators composing the lattice in three volume directions, the set of possible regimes of spatiotemporal synchronization is examined. Sufficient conditions of the stability of cluster synchronization are obtained analytically for a wide class of coupled dynamical systems with complicated individual behavior. Dependence of the necessary coupling strengths for the onset of global synchronization on the number of oscillators in each lattice direction is discussed and an approximative formula is proposed. The appearance and order of stabilization of the cluster synchronization modes with increasing coupling between the oscillators are revealed for 2-D and 3-D lattices of coupled Lur'e systems and of coupled Rossler oscillators
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