213 research outputs found
Suppression of the D'yakonov-Perel' spin relaxation mechanism for all spin components in [111] zincblende quantum wells
We apply the D'yakonov-Perel' (DP) formalism to [111]-grown zincblende
quantum wells (QWs) to compute the spin lifetimes of electrons in the
two-dimensional electron gas. We account for both bulk and structural inversion
asymmetry (Rashba) effects. We see that, under certain conditions, the spin
splitting vanishes to first order in k, which effectively suppresses the DP
spin relaxation mechanism for all spin components. We predict extended spin
lifetimes as a result, giving rise to the possibility of enhanced spin storage.
We also study [110]-grown QWs, where the effect of structural inversion
asymmetry is to augment the spin relaxation rate of the component perpendicular
to the well. We derive analytical expressions for the spin lifetime tensor and
its proper axes, and see that they are dependent on the relative magnitude of
the BIA- and SIA-induced splittings.Comment: v1: 5 pages, 2 figures, submitted to PRL v2: added 1 figure and
supporting content, PRB forma
Spin relaxation in a GaAs quantum dot embedded inside a suspended phonon cavity
The phonon-induced spin relaxation in a two-dimensional quantum dot embedded
inside a semiconductor slab is investigated theoretically. An enhanced
relaxation rate is found due to the phonon van Hove singularities. Oppositely,
a vanishing deformation potential may also result in a suppression of the spin
relaxation rate. For larger quantum dots, the interplay between the spin orbit
interaction and Zeeman levels causes the suppression of the relaxation at
several points. Furthermore, a crossover from confined to bulk-like systems is
obtained by varying the width of the slab.Comment: 5 pages, 4 figures, to apper in Phys. Rev. B (2006
Cyclotron effect on coherent spin precession of two-dimensional electrons
We investigate the spin dynamics of high-mobility two-dimensional electrons
in GaAs/AlGaAs quantum wells grown along the and directions by
time-resolved Faraday rotation at low temperatures. In measurements on the
-grown structures without external magnetic fields, we observe coherent
oscillations of the electron spin polarization about the effective spin-orbit
field. In non-quantizing magnetic fields applied normal to the sample plane,
the cyclotron motion of the electrons rotates the effective spin-orbit field.
This rotation leads to fast oscillations in the spin polarization about a
non-zero value and a strong increase in the spin dephasing time in our
experiments. These two effects are absent in the -grown structure due to
the different symmetry of its effective spin-orbit field. The measurements are
in excellent agreement with our theoretical model.Comment: 4 pages, 3 figure
Dependence of spin dephasing on initial spin polarization in a high-mobility two-dimensional electron system
We have studied the spin dynamics of a high-mobility two-dimensional electron
system in a GaAs/Al_{0.3}Ga_{0.7}As single quantum well by time-resolved
Faraday rotation and time-resolved Kerr rotation in dependence on the initial
degree of spin polarization, P, of the electrons. By increasing the initial
spin polarization from the low-P regime to a significant P of several percent,
we find that the spin dephasing time, , increases from about 20 ps to
200 ps; Moreover, increases with temperature at small spin
polarization but decreases with temperature at large spin polarization. All
these features are in good agreement with theoretical predictions by Weng and
Wu [Phys. Rev. B {\bf 68}, 075312 (2003)]. Measurements as a function of spin
polarization at fixed electron density are performed to further confirm the
theory. A fully microscopic calculation is performed by setting up and
numerically solving the kinetic spin Bloch equations, including the
D'yakonov-Perel' and the Bir-Aronov-Pikus mechanisms, with {\em all} the
scattering explicitly included. We reproduce all principal features of the
experiments, i.e., a dramatic decrease of spin dephasing with increasing
and the temperature dependences at different spin polarizations.Comment: 8 pages, 8 figures, to be published in PR
Spin relaxation dynamics of quasiclassical electrons in ballistic quantum dots with strong spin-orbit coupling
We performed path integral simulations of spin evolution controlled by the
Rashba spin-orbit interaction in the semiclassical regime for chaotic and
regular quantum dots. The spin polarization dynamics have been found to be
strikingly different from the D'yakonov-Perel' (DP) spin relaxation in bulk
systems. Also an important distinction have been found between long time spin
evolutions in classically chaotic and regular systems. In the former case the
spin polarization relaxes to zero within relaxation time much larger than the
DP relaxation, while in the latter case it evolves to a time independent
residual value. The quantum mechanical analysis of the spin evolution based on
the exact solution of the Schroedinger equation with Rashba SOI has confirmed
the results of the classical simulations for the circular dot, which is
expected to be valid in general regular systems. In contrast, the spin
relaxation down to zero in chaotic dots contradicts to what have to be expected
from quantum mechanics. This signals on importance at long time of the
mesoscopic echo effect missed in the semiclassical simulations.Comment: 14 pages, 9 figure
Effect of initial spin polarization on spin dephasing and electron g factor in a high-mobility two-dimensional electron system
We have investigated the spin dynamics of a high-mobility two-dimensional
electron system (2DES) in a GaAs--AlGaAs single quantum well by
time-resolved Faraday rotation (TRFR) in dependence on the initial degree of
spin polarization, , of the 2DES. From to %, we observe
an increase of the spin dephasing time, , by an order of magnitude,
from about 20 ps to 200 ps, in good agreement with theoretical predictions by
Weng and Wu [Phys. Rev. B {\bf 68}, 075312 (2003)]. Furthermore, by applying an
external magnetic field in the Voigt configuration, also the electron
factor is found to decrease for increasing . Fully microscopic calculations,
by numerically solving the kinetic spin Bloch equations considering the
D'yakonov-Perel' and the Bir-Aronov-Pikus mechanisms, reproduce the most
salient features of the experiments, {\em i.e}., a dramatic decrease of spin
dephasing and a moderate decrease of the electron factor with increasing
. We show that both results are determined dominantly by the Hartree-Fock
contribution of the Coulomb interaction.Comment: 4 pages, 4 figures, to be published in PR
Electron spin relaxation in bulk III-V semiconductors from a fully microscopic kinetic spin Bloch equation approach
Electron spin relaxation in bulk III-V semiconductors is investigated from a
fully microscopic kinetic spin Bloch equation approach where all relevant
scatterings, such as, the electron--nonmagnetic-impurity, electron-phonon,
electron-electron, electron-hole, and electron-hole exchange (the
Bir-Aronov-Pikus mechanism) scatterings are explicitly included. The
Elliot-Yafet mechanism is also fully incorporated. This approach offers a way
toward thorough understanding of electron spin relaxation both near and far
away from the equilibrium in the metallic regime. The dependence of the spin
relaxation time on electron density, temperature, initial spin polarization,
photo-excitation density, and hole density are studied thoroughly with the
underlying physics analyzed. In contrast to the previous investigations in the
literature, we find that: (i) In -type materials, the Elliot-Yafet mechanism
is {\em less} important than the D'yakonov-Perel' mechanism, even for the
narrow band-gap semiconductors such as InSb and InAs. (ii) The density
dependence of the spin relaxation time is nonmonotonic and we predict a {\em
peak} in the metallic regime in both -type and intrinsic materials. (iii) In
intrinsic materials, the Bir-Aronov-Pikus mechanism is found to be negligible
compared with the D'yakonov-Perel' mechanism. We also predict a peak in the
temperature dependence of spin relaxation time which is due to the nonmonotonic
temperature dependence of the electron-electron Coulomb scattering in intrinsic
materials with small initial spin polarization. (iv) In -type III-V
semiconductors, ...... (the remaining is omitted here due to the limit of
space)Comment: 25 pages, 17 figure
Multiple Scattering Theory for Two-dimensional Electron Gases in the Presence of Spin-Orbit Coupling
In order to model the phase-coherent scattering of electrons in
two-dimensional electron gases in the presence of Rashba spin-orbit coupling, a
general partial-wave expansion is developed for scattering from a cylindrically
symmetric potential. The theory is applied to possible electron flow imaging
experiments using a moveable scanning probe microscope tip. In such
experiments, it is demonstrated theoretically that the Rashba spin-orbit
coupling can give rise to spin interference effects, even for unpolarized
electrons at nonzero temperature and no magnetic field.Comment: 34 pages, 7 figure
Kinetic investigation on extrinsic spin Hall effect induced by skew scattering
The kinetics of the extrinsic spin Hall conductivity induced by the skew
scattering is performed from the fully microscopic kinetic spin Bloch equation
approach in GaAs symmetric quantum well. In the steady state, the
extrinsic spin Hall current/conductivity vanishes for the linear-
dependent spin-orbit coupling and is very small for the cubic-
dependent spin-orbit coupling. The spin precession induced by the
Dresselhaus/Rashba spin-orbit coupling plays a very important role in the
vanishment of the extrinsic spin Hall conductivity in the steady state. An
in-plane spin polarization is induced by the skew scattering, with the help of
the spin-orbit coupling. This spin polarization is very different from the
current-induced spin polarization.Comment: 5 pages, 2 figures, to be published in JPC
Spin relaxation in semiconductor quantum dots
We have studied the physical processes responsible for the spin -flip in GaAs
quantum dots. We have calculated the rates for different mechanisms which are
related to spin-orbit coupling and cause a spin-flip during the inelastic
relaxation of the electron in the dot both with and without a magnetic field.
We have shown that the zero-dimensional character of the problem when electron
wave functions are localized in all directions leads to freezing out of the
most effective spin-flip mechanisms related to the absence of the inversion
centers in the elementary crystal cell and at the heterointerface and, as a
result, to unusually low spin-flip rates.Comment: 6 pages, RevTe
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