45,135 research outputs found
Optical properties of Si/Si0.87Ge0.13 multiple quantum well wires
Nanometer-scale wires cut into a Si/Si0.87Ge0.13 multiple quantum well structure were fabricated and characterized by using photoluminescence and photoreflectance at temperatures between 4 and 20 K. It was found that, in addition to a low-energy broadband emission at around 0.8 eV and other features normally observable in photoluminescence measurements, fabrication process induced strain relaxation and enhanced electron-hole droplets emission together with a new feature at 1.131 eV at 4 K were observed. The latter was further identified as a transition related to impurities located at the Si/Si0.87Ge0.13 heterointerfaces
All-electrical control of single ion spins in a semiconductor
We propose a method for all-electrical initialization, control and readout of
the spin of single ions substituted into a semiconductor. Mn ions in GaAs form
a natural example. In the ion's ground state the Mn core spin magnetic moment
locks antiparallel to the spin and orbital magnetic moment of a bound valence
hole from the GaAs host. Direct electrical manipulation of the ion spin is
possible because electric fields manipulate the orbital wave function of the
hole, and through the spin-orbit coupling the spin is reoriented as well.
Coupling two or more ion spins can be achieved using electrical gates to
control the size of the valence hole wave function near the semiconductor
surface. This proposal for coherent manipulation of individual ionic spins and
controlled coupling of ionic spins via electrical gates alone may find
applications in extremely high density information storage and in scalable
coherent or quantum information processing.Comment: 5 pages, 3 figure
Non-Magnetic Spinguides and Spin Transport in Semiconductors
We propose the idea of a "spinguide", i.e. the semiconductor channel which is
surrounded with walls from the diluted magnetic semiconductor (DMS) with the
giant Zeeman splitting which are transparent for electrons with the one spin
polarization only. These spinguides may serve as sources of a spin-polarized
current in non-magnetic conductors, ultrafast switches of a spin polarization
of an electric current and, long distances transmission facilities of a spin
polarization (transmission distances can exceed a spin-flip length). The
selective transparence of walls leads to new size effects in transport.Comment: 4 pages, 2 figure
Nonlinear dynamics of self-sustained supersonic reaction waves: Fickett's detonation analogue
The present study investigates the spatio-temporal variability in the
dynamics of self-sustained supersonic reaction waves propagating through an
excitable medium. The model is an extension of Fickett's detonation model with
a state dependent energy addition term. Stable and pulsating supersonic waves
are predicted. With increasing sensitivity of the reaction rate, the reaction
wave transits from steady propagation to stable limit cycles and eventually to
chaos through the classical Feigenbaum route. The physical pulsation mechanism
is explained by the coherence between internal wave motion and energy release.
The results obtained clarify the physical origin of detonation wave instability
in chemical detonations previously observed experimentally.Comment: 4 pages, 3 figure
Global quark polarization in non-central collisions
Partons produced in the early stage of non-central heavy-ion collisions can
develop a longitudinal fluid shear because of unequal local number densities of
participant target and projectile nucleons. Under such fluid shear, local
parton pairs with non-vanishing impact parameter have finite local relative
orbital angular momentum along the direction opposite to the reaction plane.
Such finite relative orbital angular momentum among locally interacting quark
pairs can lead to global quark polarization along the same direction due to
spin-orbital coupling. Local longitudinal fluid shear is estimated within both
Landau fireball and Bjorken scaling model of initial parton production. Quark
polarization through quark-quark scatterings with the exchange of a thermal
gluon is calculated beyond small-angle scattering approximation in a
quark-gluon plasma. The polarization is shown to have a non-monotonic
dependence on the local relative orbital angular momentum dictated by the
interplay between electric and magnetic interaction. It peaks at a value of
relative orbital angular momentum which scales with the magnetic mass of the
exchanged gluons. With the estimated small longitudinal fluid shear in
semi-peripheral collisions at the RHIC energy, the final quark
polarization is found to be small in the weak coupling limit.
Possible behavior of the quark polarization in the strong coupling limit and
implications on the experimental detection of such global quark polarization at
RHIC and LHC are also discussed.Comment: 28 pages,11 figure
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