438 research outputs found
The Interaction in the Macroscopically Ordered Exciton State
The macroscopically ordered exciton state (MOES) - a periodic array of beads
with spatial order on a macroscopic length - appears in the external exciton
rings at low temperatures below a few Kelvin. Here, we report on the
experimental study of the interaction in the MOES. The exciton PL energy varies
in concert with the intensity along the circumference of the ring, with the
largest energy found in the brightest regions. This shows that the MOES is
characterized by the repulsive interaction and is not driven by the attractive
interaction.Comment: 3 pages, 3 figure
The Qualitative Interview in Psychology and the Study of Social Change: Sexual Identity Development, Minority Stress, and Health in the Generations Study.
Interviewing is considered a key form of qualitative inquiry in psychology that yields rich data on lived experience and meaning making of life events. Interviews that contain multiple components informed by specific epistemologies have the potential to provide particularly nuanced perspectives on psychological experience. We offer a methodological model for a multi-component interview that draws upon both pragmatic and constructivist epistemologies to examine generational differences in the experience of identity development, stress, and health among contemporary sexual minorities in the United States. Grounded in theories of life course, narrative, and intersectionality, we designed and implemented a multi-component protocol that was administered among a diverse sample of three generations of sexual minority individuals. For each component, we describe the purpose and utility, underlying epistemology, foundational psychological approach, and procedure, and we provide illustrative data from interviewees. We discuss procedures undertaken to ensure methodological integrity in process of data collection, illustrating the implementation of recent guidelines for qualitative inquiry in psychology. We highlight the utility of this qualitative multi-component interview to examine the way in which sexual minorities of distinct generations have made meaning of significant social change over the past half-century
Kinetics of the inner ring in the exciton emission pattern in GaAs coupled quantum wells
We report on the kinetics of the inner ring in the exciton emission pattern.
The formation time of the inner ring following the onset of the laser
excitation is found to be about 30 ns. The inner ring was also found to
disappear within 4 ns after the laser termination. The latter process is
accompanied by a jump in the photoluminescence (PL) intensity. The spatial
dependence of the PL-jump indicates that the excitons outside of the region of
laser excitation, including the inner ring region, are efficiently cooled to
the lattice temperature even during the laser excitation. The ring formation
and disappearance are explained in terms of exciton transport and cooling.Comment: 19 pages, 6 figure
Excitons in Electrostatic Traps
We consider in-plane electrostatic traps for indirect excitons in coupled
quantum wells, where the traps are formed by a laterally modulated gate
voltage. An intrinsic obstacle for exciton confinement in electrostatic traps
is an in-plane electric field that can lead to exciton dissociation. We propose
a design to suppress the in-plane electric field and, at the same time, to
effectively confine excitons in the electrostatic traps. We present
calculations for various classes of electrostatic traps and experimental proof
of principle for trapping of indirect excitons in electrostatic traps.Comment: 4 pages, 3 figure
Predicting Scattering Scanning Near-field Optical Microscopy of Mass-produced Plasmonic Devices
Scattering scanning near-field optical microscopy enables optical imaging and
characterization of plasmonic devices with nanometer-scale resolution well
below the diffraction limit. This technique enables developers to probe and
understand the waveguide-coupled plasmonic antenna in as-fabricated
heat-assisted magnetic recording heads. In order validate and predict results
and to extract information from experimental measurements that is physically
comparable to simulations, a model was developed to translate the simulated
electric field into expected near-field measurements using physical parameters
specific to scattering scanning near-field optical microscopy physics. The
methods used in this paper prove that scattering scanning near-field optical
microscopy can be used to determine critical sub-diffraction-limited dimensions
of optical field confinement, which is a crucial metrology requirement for the
future of nano-optics, semiconductor photonic devices, and biological sensing
where the near-field character of light is fundamental to device operation.Comment: article: 18 pages, 5 figures; SI: 15 pages, 12 figure
Pancharatnam-Berry phase in condensate of indirect excitons
We report on the observation of the Pancharatnam-Berry phase in a condensate
of indirect excitons (IXs) in a GaAs coupled quantum well structure. The
Pancharatnam-Berry phase leads to phase shifts of interference fringes in IX
interference patterns. Correlations are found between the phase shifts,
polarization pattern of IX emission, and onset of IX spontaneous coherence. The
Pancharatnam-Berry phase is acquired due to coherent spin precession in IX
condensate. The effect of the Pancharatnam-Berry phase on the IX phase pattern
is described in terms of an associated momentum.Comment: 6 pages, 5 figures + 2 pages supplemental material, 3 supplemental
figure
Origin of the inner ring in photoluminescence patterns of quantum well excitons
In order to explain and model the inner ring in photoluminescence (PL)
patterns of indirect excitons in GaAs/AlGaAs quantum wells (QWs), we develop a
microscopic approach formulated in terms of coupled nonlinear equations for the
diffusion, thermalization and optical decay of the particles. The origin of the
inner ring is unambiguously identified: it is due to cooling of indirect
excitons in their propagation from the excitation spot. We infer that in our
high-quality structures the in-plane diffusion coefficient is about 10-30cm^2/s
and the amplitude of the disorder potential is about 0.45meV.Comment: 4 pages, 3 figure
Kinetics of indirect excitons in the optically-induced exciton trap
We report on the kinetics of a low-temperature gas of indirect excitons in
the optically-induced exciton trap. The excitons in the region of laser
excitation are found to rapidly -- within 4 ns -- cool to the lattice
temperature T = 1.4 K, while the excitons at the trap center are found to be
cold -- essentially at the lattice temperature -- even during the excitation
pulse. The loading time of excitons to the trap center is found to be about 40
ns, longer than the cooling time yet shorter than the lifetime of the indirect
excitons. The observed time hierarchy is favorable for creating a dense and
cold exciton gas in optically-induced traps and for in situ control of the gas
by varying the excitation profile in space and time before the excitons
recombine.Comment: 4 pages, 3 figure
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