16,355 research outputs found
The role of excitons and trions on electron spin polarization in quantum wells
We have studied the time evolution of the electron spin polarization under
continuous photoexcitation in remotely n-doped semiconductor quantum wells. The
doped region allows us to get the necessary excess of free electrons to form
trions. We have considered electron resonant photoexcitation at free, exciton
and trion electron energy levels. Also, we have studied the relative effect of
photoexcitation energy density and doping concentration. In order to obtain the
two-dimensional density evolution of the different species, we have performed
dynamic calculations through the matrix density formalism. Our results indicate
that photoexcitation of free electron level leads to a higher spin
polarization. Also, we have found that increasing the photoexcitation energy or
diminishing the doping enhances spin polarization.Comment: 30 pages, 11 figures, 1 tabl
Evaluation of the scattering amplitude in the -channel at finite density
The scattering amplitude in the -channel is studied at
finite baryonic density in the framework of a chiral unitary approach which
successfully reproduces the meson meson phase shifts and generates the
and resonances in vacuum. We address here a new variety of mechanisms
recently suggested to modify the interaction in the medium, as well as
the role of the wave selfenergy, in addition to the wave, in the
dressing of the pion propagators.Comment: 26 pages, 17 figure
Nonlinear spin-polarized transport through a ferromagnetic domain wall
A domain wall separating two oppositely magnetized regions in a ferromagnetic
semiconductor exhibits, under appropriate conditions, strongly nonlinear I-V
characteristics similar to those of a p-n diode. We study these characteristics
as functions of wall width and temperature. As the width increases or the
temperature decreases, direct tunneling between the majority spin bands
decreases the effectiveness of the diode. This has important implications for
the zero-field quenched resistance of magnetic semiconductors and for the
design of a recently proposed spin transistor.Comment: 5 pages, 3 figure
Efecto de la dieta y la salinidad en el crecimiento poblacional de tres cepas del rotÃfero Brachionus plicatilis Muller.
Quasiparticle Breakdown and Spin Hamiltonian of the Frustrated Quantum Pyrochlore YbTiO in Magnetic Field
The frustrated pyrochlore magnet YbTiO has the remarkable
property that it orders magnetically, but has no propagating magnons over wide
regions of the Brillouin zone. Here we use inelastic neutron scattering to
follow how the spectrum evolves in cubic-axis magnetic fields. At high fields
we observe in addition to dispersive magnons also a two-magnon continuum, which
grows in intensity upon reducing the field and overlaps with the one-magnon
states at intermediate fields leading to strong renormalization of the
dispersion relations, and magnon decays. Using heat capacity measurements we
find that the low and high field regions are smoothly connected with no sharp
phase transition, with the spin gap increasing monotonically in field. Through
fits to an extensive data set we re-evaluate the spin Hamiltonian finding
dominant quantum exchange terms, which we propose are responsible for the
anomalously strong fluctuations and quasiparticle breakdown effects observed at
low fields.Comment: 5 pages main text + 19 pages supplemental materia
Trion dynamics in coupled double quantum wells. Electron density effects
We have studied the coherent dynamics of injected electrons when they are
either free or bounded both in excitons and in trions (charged excitons). We
have considered a remotely doped asymmetric double quantum well where an excess
of free electrons and the direct created excitons generate trions. We have used
the matrix density formalism to analyze the electron dynamics for different
concentration of the three species. Calculations show a significant
modification of the free electron inter-sublevel oscillations cWe have studied
the coherent dynamics of injected electrons when they are aused by electrons
bound in excitons and trions. Based on the present calculations we propose a
method to detect trions through the emitted electromagnetic radiation or the
current density.Comment: 14 pages, 13 figure
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