16 research outputs found
Optical properties of a Quantum-Dot Cascade Structure
We report on our theoretical studies of the luminescence spectra of a quantum
cascade laser where the quantum wells in the active regions are replaced by
parabolic quantum dots. We analyze the influence of shape and size of the dots
on the luminescence spectra. The emission spectra have interaction induced
blueshift which increases almost linearly with increasing electron number. The
blueshift is smaller for larger and non-circular dots. For large dots, shape of
the emission line has weak dependence on the shape of quantum dots.Comment: 4 pages, 4 figure
Probing two-subband systems in a quantizing magnetic field with non-equilibrium phonons
ICPS-26: 26th International Conferences on Physics of Semiconductors, Edinburgh, Scotland, 29 July - 2 August 2002We propose to use phonon absorption spectroscopy to study many-body gaps and phases of two-subband heterostructures in the quantum Hall regime. Implications of the spin-orbit interaction for phonon absorption in this system are considered
Two-subband system in quantizing magnetic field: Probing many-body gap by non-equilibrium phonons
We study the many-body effects in a two-subband quasi-two-dimensional
electron system in a quantizing magnetic field at filling factor three. A
manifestation of these effects in the phonon absorption spectroscopy is
discussed. The electron system is mapped onto a two-level system with the
separation between levels determined by the intersubband splitting and the
cyclotron energy. The electron-electron interaction enhances the excitation
gap, which exists at all values of the interlevel splitting. This results in a
single-peak structure of the phonon absorption rate as a function of magnetic
field, instead of the double-peak structure for non-interacting electrons.Comment: 9 pages, 3 figure
Interaction of a quantum dot with an incompressible two-dimensional electron gas
We consider a system of a incompressible quantum Hall liquid in close
proximity to a parabolic quantum dot containing a few electrons. We observe a
significant influence of the interacting electrons in the dot on the excitation
spectrum of the incompressible state in the electron plane. Our calculated
charge density indicates that unlike in the case of an impurity, interacting
electrons in the dot seem to confine the fractionally charged excitations in
the incompressible liquid.Comment: 4 pages, 4 figure
Influence of Spatial Correlations on the Lasing Threshold of Random Lasers
The lasing threshold of a random laser is computed numerically from a generic
model. It is shown that spatial correlations of the disorder in the medium
(i.e., dielectric constant) lead to an increase of the decay rates of the
eigenmodes and of the lasing threshold. This is in conflict with predictions
that such correlations should lower the threshold. While all results are
derived for photonic systems, the computed decay rate distributions also apply
to electronic systems
Spin-pairing instabilities at the coincidence of two Landau levels
The effect of interactions near the coincidence of two Landau levels with
opposite spins at filling factor 1/2 is investigated. By mapping to Composite
Fermions it is shown that the fluctuations of the gauge field induces an
effective attractive Fermion interaction. This can lead to a spin-singlet
ground state that is separated from the excited states by a gap. The magnitude
of the gap is evaluated. The results are consistent with the recently observed
half-polarized states in the FQHE at a fixed filling factor. It is suggested
that similar anomalies exist for other spin configurations in degenerate
spin-up and spin-down Landau levels. An experiment for testing the spin-singlet
state is proposed.Comment: to be published in Physical Review
Mode Repulsion and Mode Coupling in Random Lasers
We studied experimentally and theoretically the interaction of lasing modes
in random media. In a homogeneously broadened gain medium, cross gain
saturation leads to spatial repulsion of lasing modes. In an inhomogeneously
broadened gain medium, mode repulsion occurs in the spectral domain. Some
lasing modes are coupled through photon hopping or electron absorption and
reemission. Under pulsed pumping, weak coupling of two modes leads to
synchronization of their lasing action. Strong coupling of two lasing modes
results in anti-phased oscillations of their intensities.Comment: 13 pages, 4 figure
Spins, charges and currents at Domain Walls in a Quantum Hall Ising Ferromagnet
We study spin textures in a quantum Hall Ising ferromagnet. Domain walls
between ferro and unpolarized states at are analyzed with a functional
theory supported by a microscopic calculation. In a neutral wall, Hartree
repulsion prevents the appearance of a fan phase provoked by a negative
stiffness. For a charged system, electrons become trapped as solitons at the
domain wall. The size and energy of the solitons are determined by both Hartree
and spin-orbit interactions. Finally, we discuss how electrical transport takes
place through the domain wall.Comment: 4 pages, 3 figures include
Energy, interaction, and photoluminescence of spin-reversed quasielectrons in fractional quantum Hall systems
The energy and photoluminescence spectra of a two-dimensional electron gas in
the fractional quantum Hall regime are studied. The single-particle properties
of reversed-spin quasielectrons (QE's) as well as the
pseudopotentials of their interaction with one another and with Laughlin
quasielectrons (QE's) and quasiholes (QH's) are calculated. Based on the
short-range character of the QE--QE and QE--QE
repulsion, the partially unpolarized incompressible states at the filling
factors and are postulated within Haldane's
hierarchy scheme. To describe photoluminescence, the family of bound
QE states of a valence hole and QE's are
predicted in analogy to the found earlier fractionally charged excitons
QE. The binding energy and optical selection rules for both families are
compared. The QE is found radiative in contrast to the dark QE,
and the QE is found non-radiative in contrast to the bright
QE.Comment: 9 pages, 6 figure