542 research outputs found
Far-infrared absorption in parallel quantum wires with weak tunneling
We study collective and single-particle intersubband excitations in a system
of quantum wires coupled via weak tunneling. For an isolated wire with
parabolic confinement, the Kohn's theorem guarantees that the absorption
spectrum represents a single sharp peak centered at the frequency given by the
bare confining potential. We show that the effect of weak tunneling between two
parabolic quantum wires is twofold: (i) additional peaks corresponding to
single-particle excitations appear in the absorption spectrum, and (ii) the
main absorption peak acquires a depolarization shift. We also show that the
interplay between tunneling and weak perpendicular magnetic field drastically
enhances the dispersion of single-particle excitations. The latter leads to a
strong damping of the intersubband plasmon for magnetic fields exceeding a
critical value.Comment: 18 pages + 6 postcript figure
Microwave-induced magnetotransport phenomena in two-dimensional electron systems: Importance of electrodynamic effects
We discuss possible origins of recently discovered microwave induced
photoresistance oscillations in very-high-electron-mobility two-dimensional
electron systems. We show that electrodynamic effects -- the radiative decay,
plasma oscillations, and retardation effects, -- are important under the
experimental conditions, and that their inclusion in the theory is essential
for understanding the discussed and related microwave induced magnetotransport
phenomena.Comment: 5 pages, including 2 figures and 1 tabl
Structures performance, benefit, cost-study
New technology concepts and structural analysis development needs which could lead to improved life cycle cost for future high-bypass turbofans were studied. The NASA-GE energy efficient engine technology is used as a base to assess the concept benefits. Recommended programs are identified for attaining these generic structural and other beneficial technologies
Influence of shape of quantum dots on their far-infrared absorption
We investigate the effects of the shape of quantum dots on their far-infrared
absorption in an external magnetic field by a model calculation. We focus our
attention on dots with a parabolic confinement potential deviating from the
common circular symmetry, and dots having circular doughnut shape. For a
confinement where the generalized Kohn theorem does not hold we are able to
interprete the results in terms of a mixture of a center-of-mass mode and
collective modes reflecting an excitation of relative motion of the electrons.
The calculations are performed within the time-dependent Hartree approximation
and the results are compared to available experimental results.Comment: RevTeX, 16 pages with 10 postscript figures included. Submitted to
Phys. Rev.
Interfacial hydrolysis of phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate by turkey erythrocyte phospholipase C
Collective charge-density excitations of non-circular quantum dots in a magnetic field
Recent photoabsorption measurements have revealed a rich fine structure in
the collective charge-density excitation spectrum of few-electron quantum dots
in the presence of magnetic fields. We have performed systematic computational
studies of the far-infrared density response of quantum dots, using
time-dependent density-functional theory in the linear regime and treating the
dots as two-dimensional disks. It turns out that the main characteristics
observed in the experiment can be understood in terms of the electronic shell
structure of the quantum dots. However, new features arise if a breaking of the
circular symmetry of the dots is allowed, leading to an improved description of
the experimental results.Comment: 18 pages, 5 figures, submitted to Phys. Rev.
Oscillation modes of two-dimensional nanostructures within the time-dependent local-spin-density approximation
We apply the time-dependent local-spin-density approximation as general
theory to describe ground states and spin-density oscillations in the linear
response regime of two-dimensional nanostructures of arbitrary shape. For this
purpose, a frequency analysis of the simulated real-time evolution is
performed. The effect on the response of the recently proposed spin-density
waves in the ground state of certain parabolic quantum dots is considered. They
lead to the prediction of a new class of excitations, soft spin-twist modes,
with energies well below that of the spin dipole oscillation.Comment: 4 RevTex pages and 4 GIF figures, accepted in PR
Magnetization of noncircular quantum dots
We calculate the magnetization of quantum dots deviating from circular
symmetry for noninteracting electrons or electrons interacting according to the
Hartree approximation. For few electrons the magnetization is found to depend
on their number, and the shape of the dot. The magnetization is an ideal probe
into the many-electron state of a quantum dot.Comment: 11 RevTeX pages with 6 included Postscript figure
Magnetoplasmons in quantum rings
We have studied the structure and dipole charge density response of nanorings
as a function of the magnetic field using local-spin density functional theory.
Two small rings consisting of 12 and 22 electrons confined by a positively
charged background are used to represent the cases of a narrow and a wide ring.
The results are qualitatively compared with experimental data existing on
microrings and on antidots. A smaller ring containing 5 electrons is also
analyzed to allow for a closer comparison with a recent experiment on a two
electron quantum ring.Comment: Typeset using Revtex, 13 pages and 11 Postscript figure
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