436 research outputs found
Spin blockade at semiconductor/ferromagnet junctions
We study theoretically extraction of spin-polarized electrons at nonmagnetic
semiconductor/ferromagnet junctions. The outflow of majority spin electrons
from the semiconductor into the ferromagnet leaves a cloud of minority spin
electrons in the semiconductor region near the junction, forming a local
spin-dipole configuration at the semiconductor/ferromagnet interface. This
minority spin cloud can limit the majority spin current through the junction
creating a pronounced spin-blockade at a critical current. We calculate the
critical spin-blockade current in both planar and cylindrical geometries and
discuss possible experimental tests of our predictions.Comment: to be published in PR
Focusing of Spin Polarization in Semiconductors by Inhomogeneous Doping
We study the evolution and distribution of non-equilibrium electron spin
polarization in n-type semiconductors within the two-component drift-diffusion
model in an applied electric field. Propagation of spin-polarized electrons
through a boundary between two semiconductor regions with different doping
levels is considered. We assume that inhomogeneous spin polarization is created
locally and driven through the boundary by the electric field. The electric
field distribution and spin polarization distribution are calculated
numerically. We show that an initially created narrow region of spin
polarization can be further compressed and amplified near the boundary. Since
the boundary involves variation of doping but no real interface between two
semiconductor materials, no significant spin-polarization loss is expected. The
proposed mechanism will be therefore useful in designing new spintronic
devices
Modeling for Semiconductor Spintronics
We summarize semiclassical modeling methods, including drift-diffusion,
kinetic transport equation and Monte Carlo simulation approaches, utilized in
studies of spin dynamics and transport in semiconductor structures. As a review
of the work by our group, several examples of applications of these modeling
techniques are presented.Comment: 31 pages, 9 figure
Laser-controlled local magnetic field with semiconductor quantum rings
We analize theoretically the dynamics of N electrons localized in a
semiconductor quantum ring under a train of phase-locked infrared laser pulses.
The pulse sequence is designed to control the total angular momentum of the
electrons. The quantum ring can be put in states characterized by strong
currents. The local magnetic field created by these currents can be used for a
selective quantum control of single spins in semiconductor systems
Dynamics of Conversion of Conduction Electrons into a Collective Charge-Density-Wave Current
The exactly solvable model which describes the dynamics of transformation of conduction electrons into nonlinear charge-carrying excitations of charge-density waves in quasi-one-dimensional Peierls-Frohlich conductors is formulated and studied by the inverse scattering transformation method. The pair of self-trapped conduction electrons transform into a charged 2Ï€ kink localized in a single conducting chain and surrounded by dipoles in neighboring chains
Mars laser altimeter based on a single photon ranging technique
The Mars 94/96 Mission will carry, among others things, the balloon probe experiment. The balloon with the scientific cargo in the gondola underneath will drift in the Mars atmosphere, its altitude will range from zero, in the night, up to 5 km at noon. The accurate gondola altitude will be determined by an altimeter. As the Balloon gondola mass is strictly limited, the altimeter total mass and power consumption are critical; maximum allowed is a few hundred grams a few tens of mWatts of average power consumption. We did propose, design, and construct the laser altimeter based on the single photon ranging technique. Topics covered include the following: principle of operation, altimeter construction, and ground tests
Persistent and radiation-induced currents in distorted quantum rings
Persistent and radiation-induced currents in distorted narrow quantum rings
are theoretically investigated. We show that ring distorsions can be described
using a geometrical potential term. We analyse the effect of this term on the
current induced by a magnetic flux (persistent current) and by a polarized
coherent electromagnetic field (radiation-induced current). The strongest
effects in persistent currents are observed for distorted rings with a small
number of electrons. The distortion smoothes the current oscillations as a
function of the magnetic flux and changes the temperature dependence of the
current amplitude. For radiation-induced currents, the distortion induces an ac
component in the current and affects its dependence on the radiation frequency
and intensity
Electronic Transport Through a Nuclear-Spin-Polarization-Induced Quantum Wire
Electron transport in a low-dimensional structure—the nuclear-spin-polarization-induced quantum wire is theoretically studied. In the proposed system the local nuclear-spin polarization creates the effective hyperfine field that confines the electrons with the spins opposite to the hyperfine field to the regions of maximal nuclear-spin polarization. The influence of the nuclear-spin relaxation and diffusion on the electron energy spectrum and on the conductance of the quantum wire is calculated and the experimental feasibility is discussed
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