994 research outputs found
Calculations of exchange interaction in impurity band of two-dimensional semiconductors with out of plane impurities
We calculate the singlet-triplet splitting for a couple of two-dimensional
electrons in the potential of two positively charged impurities which are
located out of plane. We consider different relations between vertical
distances of impurities and and their lateral distance . Such a
system has never been studied in atomic physics but the methods, worked out for
regular two-atomic molecules and helium atom, have been found to be useful.
Analytical expressions for several different limiting configurations of
impurities are obtained an interpolated formula for intermediate range of
parameters is proposed. The -dependence of the splitting is shown to become
weaker with increasing .Comment: 14 pages, RevTeX, 5 figures. Submitted to Phys Rev.
Angular distributions of scattered excited muonic hydrogen atoms
Differential cross sections of the Coulomb deexcitation in the collisions of
excited muonic hydrogen with the hydrogen atom have been studied for the first
time. In the framework of the fully quantum-mechanical close-coupling approach
both the differential cross sections for the transitions and
-averaged differential cross sections have been calculated for exotic atom
in the initial states with the principle quantum number at relative
motion energies eV and at scattering angles
. The vacuum polarization shifts of the
-states are taken into account. The calculated in the same approach
differential cross sections of the elastic and Stark scattering are also
presented. The main features of the calculated differential cross sections are
discussed and a strong anisotropy of cross sections for the Coulomb
deexcitation is predicted.Comment: 5 pages, 9 figure
Photoluminescence Spectroscopy of the Molecular Biexciton in Vertically Stacked Quantum Dot Pairs
We present photoluminescence studies of the molecular neutral
biexciton-exciton spectra of individual vertically stacked InAs/GaAs quantum
dot pairs. We tune either the hole or the electron levels of the two dots into
tunneling resonances. The spectra are described well within a few-level,
few-particle molecular model. Their properties can be modified broadly by an
electric field and by structural design, which makes them highly attractive for
controlling nonlinear optical properties.Comment: 4 pages, 5 figures, (v2, revision based on reviewers comments,
published
Electrically tunable g-factors in quantum dot molecular spin states
We present a magneto-photoluminescence study of individual vertically stacked
InAs/GaAs quantum dot pairs separated by thin tunnel barriers. As an applied
electric field tunes the relative energies of the two dots, we observe a strong
resonant increase or decrease in the g-factors of different spin states that
have molecular wavefunctions distributed over both quantum dots. We propose a
phenomenological model for the change in g-factor based on resonant changes in
the amplitude of the wavefunction in the barrier due to the formation of
bonding and antibonding orbitals.Comment: 5 pages, 5 figures, Accepted by Phys. Rev. Lett. New version reflects
response to referee comment
Second Josephson excitations beyond mean field as a toy model for thermal pressure: exact quantum dynamics and the quantum phase model
A simple four-mode Bose-Hubbard model with intrinsic time scale separation
can be considered as a paradigm for mesoscopic quantum systems in thermal
contact. In our previous work we showed that in addition to coherent particle
exchange, a novel slow collective excitation can be identified by a series of
Holstein-Primakoff transformations. This resonant energy exchange mode is not
predicted by linear Bogoliubov theory, and its frequency is sensitive to
interactions among Bogoliubov quasi-particles; it may be referred to as a
second Josephson oscillation, in analogy to the second sound mode of liquid
Helium II. In this paper we will explore this system beyond the
Gross-Pitaevskii mean field regime. We directly compare the classical mean
field dynamics to the exact full quantum many-particle dynamics and show good
agreement over a large range of the system parameters. The second Josephson
frequency becomes imaginary for stronger interactions, however, indicating
dynamical instability of the symmetric state. By means of a generalized quantum
phase model for the full four-mode system, we then show that, in this regime,
high-energy Bogoliubov quasiparticles tend to accumulate in one pair of sites,
while the actual particles preferentially occupy the opposite pair. We
interpret this as a simple model for thermal pressure
Levy distribution in many-particle quantum systems
Levy distribution, previously used to describe complex behavior of classical
systems, is shown to characterize that of quantum many-body systems. Using two
complimentary approaches, the canonical and grand-canonical formalisms, we
discovered that the momentum profile of a Tonks-Girardeau gas, -- a
one-dimensional gas of impenetrable (hard-core) bosons, harmonically
confined on a lattice at finite temperatures, obeys Levy distribution. Finally,
we extend our analysis to different confinement setups and demonstrate that the
tunable Levy distribution properly reproduces momentum profiles in
experimentally accessible regions. Our finding allows for calibration of
complex many-body quantum states by using a unique scaling exponent.Comment: 7 pages, 6 figures, results are generalized, new examples are adde
Spin Fine Structure in Optically Excited Quantum Dot Molecules
The interaction between spins in coupled quantum dots is revealed in distinct
fine structure patterns in the measured optical spectra of InAs/GaAs double
quantum dot molecules containing zero, one, or two excess holes. The fine
structure is explained well in terms of a uniquely molecular interplay of spin
exchange interactions, Pauli exclusion and orbital tunneling. This knowledge is
critical for converting quantum dot molecule tunneling into a means of
optically coupling not just orbitals, but spins.Comment: 10 pages, 7 figures, added material, (published
Effect of inter-wall surface roughness correlations on optical spectra of quantum well excitons
We show that the correlation between morphological fluctuations of two
interfaces confining a quantum well strongly suppresses a contribution of
interface disorder to inhomogeneous line width of excitons. We also demonstrate
that only taking into account these correlations one can explain all the
variety of experimental data on the dependence of the line width upon thickness
of the quantum well.Comment: 13 pages, 8 figures, Revtex4, submitted to PR
Optimization of grain quality parameters for winter rye breeding
The purpose of this work was to evaluate the phenotypic variability of grain quality indicators and to identify the set of the most informative indicators for the selection of different use varieties of winter rye. The research was carried out in Tatar Scientific Research Institute of Agriculture – Subdivision of the “Kazan Scientific Center of Russian Academy of Sciences” in 2001–2015 on 15 varieties of winter rye. Twenty parameters defining quality of grain and raw value were estimated: technological indicators (thousand grain mass, full-scale weight and grain uniformity), parameters preharvest sprouting (falling number, rate of amylogram, temperature of peak of starch gelatinization), kinematic water extract viscosity (WEV) of grain meal, baking properties (organoleptic assessment of trial baking bread). The greatest influence of genotype was found on WEV (34.8 %) and protein content (27.8 %). These features should be primarily the subject of phenotypic evaluation in the breeding process. Phenotypic variability of criteria of carbohydrate-amylase complex, α-amylases activity and technological parameters was determined predominantly (68.6…82.5 %) by environmental factors. There was no significant relationship between falling number and protein content. The falling number correlated with the rate of amylogram and the temperature of gelatinization. Positive conjugation of the average power of WEV with the rate of amylogram and falling number was found. On the basis of a prolonged phenotypic evaluation using principal component analysis we have optimized the analyzed indicators of quality properties of winter rye grain. For breeding evaluation of winter rye it is proposed to use four integral indi cators having the greatest weight load: protein content, falling number, water extract viscosity and thousand grain mass. This complex of features will provide objectivity and completeness of the evaluation of the breeding material. It was shown that the kinematic viscosity of the water extract should become an important selection index, both for determining the baking qualities of rye, and for revealing the fodder grain advantages
Oscillons: an encounter with dynamical chaos in 1953?
We present evidences that Ben F. Laposky (1914-2000) might have been the
first person who created a family of nonlinear analog circuits that allowed him
to observe chaotic attractors and other trademarks of nonlinear science as
early as 1953.Comment: accepted to Chao
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