177 research outputs found
Drift-Diffusion Approach to Spin-Polarized Transport
We develop a drift-diffusion equation that describes electron spin
polarization density in two-dimensional electron systems. In our approach,
superpositions of spin-up and spin-down states are taken into account, what
distinguishes our model from the traditional two-component drift-diffusion
approximation. The Dresselhaus and Rashba spin-orbit coupling mechanisms are
incorporated into consideration, as well as an applied electric field. The
derived equation is applied to the modelling of relaxation of homogeneous spin
polarization. Our results are consistent with previous studies
Spin memristive systems
Recently, in addition to the well-known resistor, capacitor and inductor, a
fourth passive circuit element, named memristor, has been identified following
theoretical predictions. The model example used in such case consisted in a
nanoscale system with coupled ionic and electronic transport. Here, we discuss
a system whose memristive behaviour is based entirely on the electron spin
degree of freedom which allows for a more convenient control than the ionic
transport in nanostructures. An analysis of time-dependent spin transport at a
semiconductor/ferromagnet junction provides a direct evidence of memristive
behaviour. Our scheme is fundamentally different from previously discussed
schemes of memristive devices and broadens the possible range of applications
of semiconductor spintronics
Spin injection and accumulation in inhomogeneous semiconductors
We present a study of spin transport in charge and spin inhomogeneous
semiconductor systems. In particular, we investigate the propagation of
spin-polarized electrons through a boundary between two semiconductor regions
with different doping concentrations. We use a theoretical and numerical
method, presented in this paper, based on a self-consistent treatment of a
two-component version of the Boltzmann transport equation. We show that
space-charge effects strongly influence the spin transport properties, in
particular giving rise to pronounced spin accumulation and spin density
enhancement.Comment: 4 page
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
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
Spin polarization control by electric stirring: proposal for a spintronic device
We propose a spintronic device to generate spin polarization in a mesoscopic
region by purely electric means. We show that the spin Hall effect in
combination with the stirring effect are sufficient to induce measurable spin
polarization in a closed geometry. Our device structure does not require the
application of magnetic fields, external radiation or ferromagnetic leads, and
can be implemented in standard semiconducting materials
Solid-state memcapacitive system with negative and diverging capacitance
We suggest a possible realization of a solid-state memory capacitive
(memcapacitive) system. Our approach relies on the slow polarization rate of a
medium between plates of a regular capacitor. To achieve this goal, we consider
a multi-layer structure embedded in a capacitor. The multi-layer structure is
formed by metallic layers separated by an insulator so that non-linear
electronic transport (tunneling) between the layers can occur. The suggested
memcapacitor shows hysteretic charge-voltage and capacitance-voltage curves,
and both negative and diverging capacitance within certain ranges of the field.
This proposal can be easily realized experimentally, and indicates the
possibility of information storage in memcapacitive devices
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
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