2,534 research outputs found
Optical characteristics of single wavelength-tunable InAs/InGaAsP/InP(100) quantum dots emitting at 1.55 um
We have studied the emission properties of individual InAs quantum dots (QDs)
grown in an InGaAsP matrix on InP(100) by metal-organic vapor-phase epitaxy.
Low-temperature microphotoluminescence spectroscopy shows emission from single
QDs around 1550 nm with characteristic exciton-biexciton behavior, and a
biexciton antibinding energy of more than 2 meV. Temperature-dependent
measurements reveal negligible optical-phonon induced broadening of the exciton
line up to 50 K, and emission from the exciton state clearly persists above 70
K. Furthermore, we find no measurable polarized fine structure splitting of the
exciton state within the experimental precision. These results are encouraging
for the development of a controllable photon source for fiber-based quantum
information and cryptography systems.Comment: 3 pages, 4 figures, submitted AP
Charged exciton emission at 1.3 m from single InAs quantum dots grown by metalorganic chemical vapor deposition
We have studied the emission properties of self-organized InAs quantum dots
(QDs) grown in an InGaAs quantum well by metalorganic chemical vapor
deposition. Low-temperature photoluminescence spectroscopy shows emission from
single QDs around 1300 nm; we clearly observe the formation of neutral and
charged exciton and biexciton states, and we obtain a biexciton binding energy
of 3.1 meV. The dots exhibit an s-p shell splitting of approximately 100 meV,
indicating strong confinement.Comment: 3 pages, 3 figures, submitted AP
Fine structure and magneto-optics of exciton, trion, and charged biexciton states in single InAs quantum dots emitting at 1.3 um
We present a detailed investigation into the optical characteristics of
individual InAs quantum dots (QDs) grown by metalorganic chemical vapor
deposition, with low temperature emission in the telecoms window around 1300
nm. Using micro-photoluminescence (PL) spectroscopy we have identified neutral,
positively charged, and negatively charged exciton and biexciton states.
Temperature-dependent measurements reveal dot-charging effects due to
differences in carrier diffusivity. We observe a pronounced linearly polarized
splitting of the neutral exciton and biexciton lines (~250 ueV) resulting from
asymmetry in the QD structure. This asymmetry also causes a mixing of the
excited trion states which is manifested in the fine structure and polarization
of the charged biexciton emission; from this data we obtain values for the
ratio between the anisotropic and isotropic electron-hole exchange energies of
(Delta1)/(Delta0)= 0.2--0.5. Magneto-PL spectroscopy has been used to
investigate the diamagnetic response and Zeeman splitting of the various
exciton complexes. We find a significant variation in g-factor between the
exciton, the positive biexciton, and the negative biexciton; this is also
attributed to anisotropy effects and the difference in lateral extent of the
electron and hole wavefunctions.Comment: 7 pages, 6 figures, submitted to Phys. Rev.
Coulomb effects in semiconductor quantum dots
Coulomb correlations in the optical spectra of semiconductor quantum dots are
investigated using a full-diagonalization approach. The resulting multi-exciton
spectra are discussed in terms of the symmetry of the involved states.
Characteristic features of the spectra like the nearly equidistantly spaced
s-shell emission lines and the approximately constant p-shell transition
energies are explained using simplified Hamiltonians that are derived taking
into account the relative importance of various interaction contributions.
Comparisons with previous results in the literature and their interpretation
are made.Comment: 7 pages, 2 figure
Some constructions of almost para-hyperhermitian structures on manifolds and tangent bundles
In this paper we give some examples of almost para-hyperhermitian structures
on the tangent bundle of an almost product manifold, on the product manifold
, where is a manifold endowed with a mixed 3-structure
and on the circle bundle over a manifold with a mixed 3-structure.Comment: 10 pages; This paper has been presented in the "4th German-Romanian
Seminar on Geometry" Dortmund, Germany, 15-18 July 200
Relativity and the low energy nd Ay puzzle
We solve the Faddeev equation in an exactly Poincare invariant formulation of
the three-nucleon problem. The dynamical input is a relativistic
nucleon-nucleon interaction that is exactly on-shell equivalent to the high
precision CDBonn NN interaction. S-matrix cluster properties dictate how the
two-body dynamics is embedded in the three-nucleon mass operator. We find that
for neutron laboratory energies above 20 MeV relativistic effects on Ay are
negligible. For energies below 20 MeV dynamical effects lower the nucleon
analyzing power maximum slightly by 2% and Wigner rotations lower it further up
to 10 % increasing thus disagreement between data and theory. This indicates
that three-nucleon forces must provide an even larger increase of the Ay
maximum than expected up to now.Comment: 29 pages, 2 ps figure
The alpha-particle based on modern nuclear forces
The Faddeev-Yakubovsky equations for the alpha-particle are solved. Accurate
results are obtained for several modern NN interaction models, which include
charge-symmetry breaking effects in the NN force, nucleon mass dependences as
well as the Coulomb interaction. These models are augmented by three-nucleon
forces of different types and adjusted to the 3N binding energy. Our results
are close to the experimental binding energy with a slight overbinding. Thus
there is only little room left for the contribution of possible 4N interactions
to the alpha-particle binding energy. We also discuss model dependences of the
binding energies and the wave functions.Comment: 22 pages REVTeX 4, 12 figures, table with TM parameters added, typos
corrected, version as published in PR
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