2,485 research outputs found
Diffuse Reflection Diameter in Simple Polygons
We prove a conjecture of Aanjaneya, Bishnu, and Pal that the minimum number
of diffuse reflections sufficient to illuminate the interior of any simple
polygon with walls from any interior point light source is . Light reflecting diffusely leaves a surface in all directions,
rather than at an identical angle as with specular reflections.Comment: To appear in Discrete Applied Mathematic
Highly polarized injection luminescence in forward-biased ferromagnetic-semiconductor junctions at low spin polarization of current
We consider electron tunneling from a nonmagnetic -type semiconductor
(-S) into a ferromagnet (FM) through a very thin forward-biased Schottky
barrier resulting in efficient extraction of electron spin from a thin -S
layer near FM-S interface at low spin polarization of the current. We show that
this effect can be used for an efficient polarization radiation source in a
heterostructure where the accumulated spin polarized electrons are injected
from -S and recombine with holes in a quantum well. The radiation
polarization depends on a bias voltage applied to the FM-S junction.Comment: 4 pages, 2 figure
Giant Magneto-Oscillations of Electric-Field-Induced Spin Polarization in 2DEG
We consider a disordered two-dimensional electron gas with spin-orbit
coupling placed in a perpendicular magnetic field and calculate the magnitude
and direction of the electric-field-induced spin polarization. We find that in
strong magnetic fields the polarization becomes an oscillatory function of the
magnetic field and that the amplitude of these oscillations is parametrically
larger than the polarization at zero magnetic field. We show that the enhanced
amplitude of the polarization is a consequence of strong electron-hole
asymmetry in a quantizing magnetic field.Comment: 6 pages, 3 figure
New Origin For Spin Current And Current-Induced Spin Precession In Magnetic Multilayers
In metallic ferromagnets, an electric current is accompanied by a flux of
angula r momentum, also called spin current. In multilayers, spatial variations
of the spin current correspond to drive torques exerted on a magnetic layer.
These torq ues result in spin precession above a certain current threshold. The
usual kind of spin current is associated with translation of the spin-up and
spin-down Ferm i surfaces in momentum space. We discuss a different kind of
spin current, assoc iated with expansion and contraction of the Fermi surfaces.
It is more nonlocal in nature, and may exist even in locations where the
electrical current density is zero. It is larger than the usual spin current,
in a ratio of 10 or 100, and is dominant in most cases. The new spin current is
proportional to the differenc e Delta-mu = 0.001 eV between spin-up and
spin-down Fermi levels, averaged over the entire Fermi surface. Conduction
processes, spin relaxation, and spin-wave emission in the multilayer can be
described by an equivalent electrical circuit resembling an unbalanced dc
Wheatstone bridge. And Delta-mu corresponds to the output voltage of the
bridge.Comment: 5 pages, 3 figures. To appear in J. Appl. Phys., vol. 89, May 15,
200
Geometrical effects on spin injection: 3D spin drift diffusion model
We discuss a three-dimensional (3D) spin drift diffusion (SDD) model to
inject spin from a ferromagnet (FM) to a normal metal (N) or semiconductor
(SC). Using this model we investigate the problem of spin injection into
isotropic materials like GaAs and study the effect of FM contact area and SC
thickness on spin injection. We find that in order to achieve detectable spin
injection a small contact area or thick SC samples are essential for direct
contact spin injection devices. We investigate the use of thin metal films (Cu)
proposed by S.B. Kumar et al. and show that they are an excellent substitute
for tunnelling barriers (TB) in the regime of small contact area. Since most
tunnelling barriers are prone to pinhole defects, we study the effect of
pinholes in AlO tunnelling barriers and show that the reduction in the
spin-injection ratio () is solely due to the effective area of the
pinholes and there is no correlation between the number of pinholes and the
spin injection ratio.Comment: 5 pages, 6 figures. Accepted by JA
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