1,730 research outputs found
Energy levels and far-infrared spectroscopy for two electrons in a semiconductor nanoring
The effects of electron-electron interaction of a two-electron nanoring on
the energy levels and far-infrared (FIR) spectroscopy have been investigated
based on a model calculation which is performed within the exactly numerical
diagonalization. It is found that the interaction changes the energy spectra
dramatically, and also shows significant influence on the FIR spectroscopy. The
crossings between the lowest spin-singlet and triplet states induced by the
coulomb interaction are clearly revealed. Our results are related to the
experiment recently carried out by A. Lorke et al. [Phys. Rev. Lett. 84, 2223
(2000)].Comment: 17 pages, 6 figures, revised and accepted by Phys. Rev. B (Dec. 15
A possible cooling effect in high temperature superconductors
We show that an adiabatic increase of the supercurrent along a superconductor
with lines of nodes of the order parameter on the Fermi surface can result in a
cooling effect. The maximum cooling occurs if the supercurrent increases up to
its critical value. The effect can also be observed in a mixed state of a bulk
sample. An estimate of the energy dissipation shows that substantial cooling
can be performed during a reasonable time even in the microkelvin regime.Comment: 5 pages, to appear in Phys. Rev.
Electron locking in semiconductor superlattices
We describe a novel state of electrons and phonons arising in semiconductor
superlattices (SSL) due to strong electron-phonon interactions. These states
are characterized by a localization of phonons and a self-trapping or locking
of electrons in one or several quantum wells due to an additional,
deformational potential arising around these locking wells in SSL. The effect
is enhanced in a longitudinal magnetic field.
Using the tight-binding and adiabatic approximations the whole energy
spectrum of the self-trapped states is found and accurate, analytic expressions
are included for strong electron-phonon coupling. Finally, we discuss possible
experiments which may detect these predicted self-trapped states.Comment: 8 pages, 2 figures. Please note that the published article has the
title 'Electron locking in layered structures by a longitudinal magnetic
field
Inelastic light scattering and the excited states of many-electron quantum dots
A consistent calculation of resonant inelastic (Raman) scattering amplitudes
for relatively large quantum dots, which takes account of valence-band mixing,
discrete character of the spectrum in intermediate and final states, and
interference effects, is presented. Raman peaks in charge and spin channels are
compared with multipole strengths and with the density of energy levels in
final states. A qualitative comparison with the available experimental results
is given.Comment: 5 pages, accepted in J. Phys.: Condens. Matte
Mean parameter model for the Pekar-Fr\"{o}hlich polaron in a multilayered heterostructure
The polaron energy and the effective mass are calculated for an electron
confined in a finite quantum well constructed of
layers. To simplify the study we suggest a model in which parameters of a
medium are averaged over the ground-state wave function. The rectangular and
the Rosen-Morse potential are used as examples.
To describe the confined electron properties explicitly to the second order
of perturbations in powers of the electron-phonon coupling constant we use the
exact energy-dependent Green function for the Rosen-Morse confining potential.
In the case of the rectangular potential, the sum over all intermediate virtual
states is calculated. The comparison is made with the often used leading term
approximation when only the ground-state is taken into account as a virtual
state. It is shown that the results are quite different, so the incorporation
of all virtual states and especially those of the continuous spectrum is
essential.
Our model reproduces the correct three-dimensional asymptotics at both small
and large widths. We obtained a rather monotonous behavior of the polaron
energy as a function of the confining potential width and found a peak of the
effective mass. The comparison is made with theoretical results by other
authors. We found that our model gives practically the same (or very close)
results as the explicit calculations for potential widths .Comment: 12 pages, LaTeX, including 5 PS-figures, subm. to Phys. Rev. B, new
data are discusse
Localized magnetoplasmon modes arising from broken translational symmetry in semiconductor superlattices
The electromagnetic propagator associated with the localized collective
magnetoplasmon excitations in a semiconductor superlattice with broken
translational symmetry, is calculated analytically within linear response
theory. We discuss the properties of these collective excitations in both
radiative and non-radiative regimes of the electromagnetic spectra. We find
that low frequency retarded modes arise when the surface density of carriers at
the symmetry breaking layer is lower than the density at the remaining layers.
Otherwise a doublet of localized, high-frequency magnetoplasmon-like modes
occurs.Comment: Revtex file + separate pdf figure
Magnetoplasmon excitations in an array of periodically modulated quantum wires
Motivated by the recent experiment of Hochgraefe et al., we have investigated
the magnetoplasmon excitations in a periodic array of quantum wires with a
periodic modulation along the wire direction. The equilibrium and dynamic
properties of the system are treated self-consistently within the
Thomas-Fermi-Dirac-von Weizsaecker approximation. A calculation of the
dynamical response of the system to a far-infrared radiation field reveals a
resonant anticrossing between the Kohn mode and a finite-wavevector
longitudinal excitation which is induced by the density modulation along the
wires. Our theoretical calculations are found to be in excellent agreement with
experiment.Comment: 9 pages, 8 figure
Picosecond time-resolved, polarized fluorescence decay of phycobilisomes and constituent biliproteins isolated from Mastigocladus laminosus
Theoretical calculations of the primary defects induced by pions and protons in SiC
In the present work, the bulk degradation of SiC in hadron (pion and proton)
fields, in the energy range between 100 MeV and 10 GeV, is characterised
theoretically by means of the concentration of primary defects per unit
fluence. The results are compared to the similar ones corresponding to diamond,
silicon and GaAs.Comment: 9 pages, 2 figures, in press to Nuclear Instruments and Methods in
Physics Research A v2 - modified title, and major revision
Structure and optical properties of silicon layers with GaSb nanocrystals created by ion-beam synthesis
We have studied the ion-beam synthesis of GaSb nanocrystals in Si by high-fluence implantation of Sb and Ga ions followed by thermal annealing. RBS, TEM/TED, RS, and photoluminescence (PL) were employed to characterize the implanted layers. It was found that the nanocrystals size increases from 5 to 60 nm in the samples annealed at 900 8Cup to 20–90 nm in the samples annealed at 1100 8C. An existence of significant mechanical stresses within implanted layers has been detected. The stress values have been calculated from the shift of the Si first order Raman band. For the samples annealed at 900 8C a broad band in the spectral region of about
0.75–1.05 eV is detected in the PL spectra. The nature of this PL band is discussed
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