306 research outputs found
Non-equilibrium spin polarization effects in spin-orbit coupling system and contacting metallic leads
We study theoretically the current-induced spin polarization effect in a
two-terminal mesoscopic structure which is composed of a semiconductor
two-dimensional electron gas (2DEG) bar with Rashba spin-orbit (SO) interaction
and two attached ideal leads. The nonequilibrium spin density is calculated by
solving the scattering wave functions explicitly within the ballistic transport
regime. We found that for a Rashba SO system the electrical current can induce
spin polarization in the SO system as well as in the ideal leads. The induced
polarization in the 2DEG shows some qualitative features of the intrinsic spin
Hall effect. On the other hand, the nonequilibrium spin density in the ideal
leads, after being averaged in the transversal direction, is independent of the
distance measured from the lead/SO system interface, except in the vicinity of
the interface. Such a lead polarization effect can even be enhanced by the
presence of weak impurity scattering in the SO system and may be detectable in
real experiments.Comment: 6 pages,5 figure
Quantifying spin Hall angles from spin pumping: Experiments and Theory
Spin Hall effects intermix spin and charge currents even in nonmagnetic
materials and, therefore, ultimately may allow the use of spin transport
without the need for ferromagnets. We show how spin Hall effects can be
quantified by integrating permalloy/normal metal (N) bilayers into a coplanar
waveguide. A dc spin current in N can be generated by spin pumping in a
controllable way by ferromagnetic resonance. The transverse dc voltage detected
along the permalloy/N has contributions from both the anisotropic
magnetoresistance (AMR) and the spin Hall effect, which can be distinguished by
their symmetries. We developed a theory that accounts for both. In this way, we
determine the spin Hall angle quantitatively for Pt, Au and Mo. This approach
can readily be adapted to any conducting material with even very small spin
Hall angles.Comment: 4 pages, 4 figure
Temperature dependence of D'yakonov-Perel' spin relaxation in zinc blende semiconductor quantum structures
The D'yakonov-Perel' mechanism, intimately related to the spin splitting of
the electronic states, usually dominates the spin relaxation in zinc blende
semiconductor quantum structures. Previously it has been formulated for the two
limiting cases of low and high temperatures. Here we extend the theory to give
an accurate description of the intermediate regime which is often relevant for
room temperature experiments. Employing the self-consistent multiband envelope
function approach, we determine the spin splitting of electron subbands in
n-(001) zinc blende semiconductor quantum structures. Using these results we
calculate spin relaxation rates as a function of temperature and obtain
excellent agreement with experimental data.Comment: 9 pages, 4 figure
Spin dephasing and photoinduced spin diffusion in high-mobility 110-grown GaAs-AlGaAs two-dimensional electron systems
We have studied spin dephasing and spin diffusion in a high-mobility
two-dimensional electron system, embedded in a GaAs/AlGaAs quantum well grown
in the [110] direction, by a two-beam Hanle experiment. For very low excitation
density, we observe spin lifetimes of more than 16 ns, which rapidly decrease
as the pump intensity is increased. Two mechanisms contribute to this decrease:
the optical excitation produces holes, which lead to a decay of electron spin
via the Bir-Aranov-Pikus mechanism and recombination with spin-polarized
electrons. By scanning the distance between the pump and probe beams, we
observe the diffusion of spin-polarized electrons over more than 20 microns.
For high pump intensity, the spin polarization in a distance of several microns
from the pump beam is larger than at the pump spot, due to the reduced
influence of photogenerated holes.Comment: 4 pages, 3 figure
Kinetic magnetoelectric effect in a 2D semiconductor strip due to boundary-confinement induced spin-orbit coupling
In a thin strip of a two-dimensional semiconductor electronic system,
spin-orbit coupling may be induced near both edges of the strip due to the
substantial spatial variation of the confining potential in the boundary
regions. In this paper we show that, in the presence of boundary-confinement
induced spin-orbit coupling, a longitudinal charge current circulating through
a 2D semiconductor strip may cause \textit{strong} non-equilibrium spin
accumulation near both edges of the strip. The spins will be polarized along
the normal of the 2DEG plane but in opposite directions at both edges of the
strip. This phenomenon is essentially a kinetic magnetoelectric effect from the
theoretical points of view, but it manifests in a very similar form as was
conceived in a spin Hall effect.Comment: 7 pages, 4 fig
Ab initio calculation of intrinsic spin Hall effect in semiconductors
Relativistic band theoretical calculations reveal that intrinsic spin Hall
conductivity in hole-doped archetypical semiconductors Ge, GaAs and AlAs is
large , showing the possibility of spin
Hall effect beyond the four band Luttinger Hamiltonian. The calculated
orbital-angular-momentum (orbital) Hall conductivity is one order of magnitude
smaller, indicating no cancellation between the spin and orbital Hall effects
in bulk semiconductors. Furthermore, it is found that the spin Hall effect can
be strongly manipulated by strains, and that the spin Hall conductivity in
the semiconductors is large in pure as well as doped semiconductors.Comment: Phys. Rev. Lett. (accepted
Long range scattering effects on spin Hall current in -type bulk semiconductors
Employing a nonequilibrium Green's function approach, we examine the effects
of long-range hole-impurity scattering on spin-Hall current in -type bulk
semiconductors within the framework of the self-consistent Born approximation.
We find that, contrary to the null effect of short-range scattering on
spin-Hall current, long-range collisions do produce a nonvanishing contribution
to the spin-Hall current, which is independent of impurity density in the
diffusive regime and relates only to hole states near the Fermi surface. The
sign of this contribution is opposite to that of the previously predicted
disorder-independent spin-Hall current, leading to a sign change of the total
spin-Hall current as hole density varies. Furthermore, we also make clear that
the disorder-independent spin-Hall effect is a result of an interband
polarization directly induced by the dc electric field with contributions from
all hole states in the Fermi sea.Comment: 9 pages, 1 figur
Analysis of phonon-induced spin relaxation processes in silicon
We study all of the leading-order contributions to spin relaxation of
\textit{conduction} electrons in silicon due to the electron-phonon
interaction. Using group theory, perturbation method and rigid-ion
model, we derive an extensive set of matrix element expressions for all of the
important spin-flip transitions in the multi-valley conduction band. The
scattering angle has an explicit dependence on the electron wavevectors, phonon
polarization, valley position and spin orientation of the electron. Comparison
of the derived analytical expressions with results of empirical pseudopotential
and adiabatic band charge models shows excellent agreement.Comment: 30 pages,10 figure
Zero-field spin splitting in a two-dimensional electron gas with the spin-orbit interaction revisited
We consider a two-dimensional electron gas (2DEG) with the Rashba spin-orbit
interaction (SOI) in presence of a perpendicular magnetic field. We derive
analytical expressions of the density of states (DOS) of a 2DEG with the Rashba
SOI in presence of magnetic field by using the Green's function technique. The
DOS allows us to obtain the analytical expressions of the magnetoconductivities
for spin-up and spin-down electrons. The conductivities for spin-up and
spin-down electrons oscillate with different frequencies and gives rise to the
beating patterns in the amplitude of the Shubnikov de Hass (SdH) oscillations.
We find a simple equation which determines the zero-field spin splitting energy
if the magnetic field corresponding to any beat node is known from the
experiment. Our analytical results reproduce well the experimentally observed
non-periodic beating patterns, number of oscillations between two successive
nodes and the measured zero-field spin splitting energy.Comment: 5 pages, 2 figure
Spin Hall effect in clean two dimensional electron gases with Rashba spin-orbit coupling
We study the spin polarization induced by a current flow in clean two
dimensional electron gases with Rashba spin-orbit coupling. This geometric
effect originates from special properties of the electron's scattering at the
edges of the sample. In wide samples, the spin polarization has it largest
value at low energies (close to the bottom of the band) and goes to zero at
higher energies. In this case, the spin polarization is dominated by the
presence of evanescent modes which have an explicit spin component outside the
plane. In quantum wires, on the other hand, the spin polarization is dominated
by interference effects induced by multiple scattering at the edges. Here, the
spin polarization is quite sensitive to the value of the Fermi energy,
especially close to the point where a new channel opens up. We analyzed
different geometries and found that the spin polarization can be strongly
enhanced.Comment: 10 pages, 13 figures, high quality figures available upon reques
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