1,530 research outputs found
Order-disorder transition in nanoscopic semiconductor quantum rings
Using the path integral Monte Carlo technique we show that semiconductor
quantum rings with up to six electrons exhibit a temperature, ring diameter,
and particle number dependent transition between spin ordered and disordered
Wigner crystals. Due to the small number of particles the transition extends
over a broad temperature range and is clearly identifiable from the electron
pair correlation functions.Comment: 4 pages, 5 figures, For recent information on physics of small
systems see http://www.smallsystems.d
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
Gamow Shell Model Description of Neutron-Rich Nuclei
This work presents the first continuum shell-model study of weakly bound
neutron-rich nuclei involving multiconfiguration mixing. For the
single-particle basis, the complex-energy Berggren ensemble representing the
bound single-particle states, narrow resonances, and the non-resonant continuum
background is taken. Our shell-model Hamiltonian consists of a one-body finite
potential and a zero-range residual two-body interaction. The systems with two
valence neutrons are considered. The Gamow shell model, which is a
straightforward extension of the traditional shell model, is shown to be an
excellent tool for the microscopic description of weakly bound systems. It is
demonstrated that the residual interaction coupling to the particle continuum
is important; in some cases, it can give rise to the binding of a nucleus.Comment: 4 pages, More realistic s.p. energies used than in the precedent
versio
Collective Excitations Spectrum in Density Modulated One-Dimensional Electron Gas in a Magnetic Field
We determine the collective excitations spectrum and discuss the numerical
results for a parabolically confined density modulated quasi-one dimensional
electron gas (1DEG) in the presence of an external magnetic field. We derive
the inter-and intra-band magnetoplasmon spectrum within the Self Consistent
Field (SCF) approach. In this work we focus on magnetoplasmon oscillations in
this system and as such results are presented for the intra-Landau-band
magnetoplasmon spectrum that exhibits oscillatory behavior, these oscillations
are not with constant period in 1/B and are significantly effected at low B and
corresponding high 1/B.Comment: 10 pages, 2 figure
Magneto infra-red absorption in high electronic density GaAs quantum wells
Magneto infra-red absorption measurements have been performed in a highly
doped GaAs quantum well which has been lifted off and bonded to a silicon
substrate, in order to study the resonant polaron interaction. It is found that
the pinning of the cyclotron energy occurs at an energy close to that of the
transverse optical phonon of GaAs. This unexpected result is explained by a
model taking into account the full dielectric constant of the quantum well.Comment: 4 pages, 4 figures, to be published in Phys. Rev. Let
Analysis of the stability of InGaN/GaN multiquantum wells against ion beam intermixing
Ion-induced damage and intermixing was evaluated in InGaN/GaN multi-quantum wells (MQWs) using 35 keV N+ implantation at room temperature. In situ ion channeling measurements show that damage builds up with a similar trend for In and Ga atoms, with a high threshold for amorphization. The extended defects induced during the implantation, basal and prismatic stacking faults, are uniformly distributed across the quantum well structure. Despite the extremely high fluences used (up to 4 ×1016 cm-2), the InGaN MQWs exhibit a high stability against ion beam mixing
FÖRSTER TRANSFER CALCULATIONS BASED ON CRYSTAL STRUCTURE DATA FROM Agmenellum quadruplicatum C-PHYCOCYANIN
Excitation energy transfer in C-phycocyanin is modeled using the Forster inductive resonance mechanism. Detailed calculations are carried out using coordinates and orientations of the chromophores derived from X-ray crystallographic studies of C-phycocyanin from two different species (Schirmer et al, J. Mol. Biol. 184, 257–277 (1985) and ibid., 188, 651-677 (1986)). Spectral overlap integrals are estimated from absorption and fluorescence spectra of C-phycocyanin of Mastigocladus laminosus and its separated subunits. Calculations are carried out for the β-subunit, αβ-monomer, (αβ)3-trimer and (αβ)0-hexamer species with the following chromophore assignments: β155 = 's’(sensitizer), β84 =‘f (fluorescer) and α84 =‘m’(intermediate):]:. The calculations show that excitation transfer relaxation occurs to 3=98% within 200 ps in nearly every case; however, the rates increase as much as 10-fold for the higher aggregates. Comparison with experimental data on fluorescence decay and depolarization kinetics from the literature shows qualitative agreement with these calculations. We conclude that Forster transfer is sufficient to account for all of the observed fluorescence properties of C-phycocyanin in aggregation states up to the hexamer and in the absence of linker polypeptides
- …