52 research outputs found
Angular harmonics of the excitonic polarization conversions effect
We suggest a phenomenological theory of the polarization conversions effect,
an excitonic analog of the first-order spatial dispersion phenomena which is,
however, observed in the photoluminescence rather than in the passing light.
The optical polarization response of a model system of electrically neutral
quantum dots subject to the magnetic field along the growth axis was calculated
by means of the pseudospin method. All possible forms of the polarization
response are determined by nine different field-dependent coefficients which
represent, therefore, a natural basis for classification of a variety of
conversions. Existing experimental data can be well inscribed in this
classification scheme. Predictions were made regarding two effects which have
not been addressed experimentally.Comment: 14 pages, 1 figure, 1 tabl
Linear polarization of the photoluminescence of quantum wells
The degree and orientation of the magnetic-field induced linear polarization
of the photoluminescence from a wide range of heterostructures containing
(Cd,Mn)Te quantum wells between (Cd,Mn,Mg)Te barriers has been studied as a
function of detection photon energy, applied magnetic field strength and
orientation in the quantum well plane. A theoretical description of this effect
in terms of an in-plane deformation acting on the valence band states is
presented and is verified by comparison with the experimental data. We
attempted to identify clues to the microscopic origin of the valence band spin
anisotropy and to the mechanisms which actually determine the linear
polarization of the PL in the quantum wells subject to the in-plane magnetic
field. The conclusions of the present paper apply in full measure to
non-magnetic QWs as well as ensembles of disk-like QDs with shape and/or strain
anisotropy.Comment: 21 pages, 10 figure
The 1/N Expansion in Noncommutative Quantum Mechanics
We study the 1/N expansion in noncommutative quantum mechanics for the
anharmonic and Coulombian potentials. The expansion for the anharmonic
oscillator presented good convergence properties, but for the Coulombian
potential, we found a divergent large N expansion when using the usual
noncommutative generalization of the potential. We proposed a modified version
of the noncommutative Coulombian potential which provides a well-behaved 1/N
expansion.Comment: v2: resided version, to appear in PRD, 18 pages, 4 figure
Suris tetrons: possible spectroscopic evidence for four-particle optical excitations of the 2D electron gas
The excitations of a two-dimensional electron gas in quantum wells with
intermediate carrier density (~10^{11} cm^{-2}), i.e., between the
exciton-trion- and the Fermi-Sea range, are so far poorly understood. We report
on an approach to bridge this gap by a magneto-photoluminescence study of
modulation-doped (Cd,Mn)Te quantum well structures. Employing their enhanced
spin splitting, we analyzed the characteristic magnetic-field behavior of the
individual photoluminescence features. Based on these results and earlier
findings by other authors, we present a new approach for understanding the
optical transitions at intermediate densities in terms of four-particle
excitations, the Suris tetrons, which were up to now only predicted
theoretically. All characteristic photoluminescence features are attributed to
emission from these quasi-particles when attaining different final states.Comment: 12 pages, 3 figure
Exciton spin decay modified by strong electron-hole exchange interaction
We study exciton spin decay in the regime of strong electron-hole exchange
interaction. In this regime the electron spin precession is restricted within a
sector formed by the external magnetic field and the effective exchange fields
triggered by random spin flips of the hole. Using Hanle effect measurements, we
demonstrate that this mechanism dominates our experiments in CdTe/(Cd,Mg)Te
quantum wells. The calculations provide a consistent description of the
experimental results, which is supported by independent measurements of the
parameters entering the model.Comment: 5 pages, 3 figure
Two-step model versus one-step model of the inter-polarization conversion and statistics of CdSe/ZnSe quantum dot elongations
The magneto-optical inter-polarization conversions by a layer of quantum dots
have been investigated. Various types of polarization response of the sample
were observed as a function of external magnetic field and of the orientation
of the sample. The full set of experimental dependences is analyzed in terms of
a one-step and a two-step model of spin evolution. The angular distribution of
the quantum dots over the directions of elongation in the plane of the sample
is taken into account in terms of the two models, and the model predictions are
compared with experimental observations
- …