375 research outputs found
Theory of electric-field-induced spin accumulation and spin current in the two-dimensional Rashba model
Based on the spin-density-matrix approach, both the electric-field-induced
spin accumulation and the spin current are systematically studied for the
two-dimensional Rashba model. Eigenmodes of spin excitations give rise to
resonances in the frequency domain. Utilizing a general and physically
well-founded definition of the spin current, we obtain results that differ
remarkably from previous findings. It is shown that there is a close
relationship between the spin accumulation and the spin current, which is due
to the prescription of a quasi-chemical potential and which does not result
from a conservation law. Physical ambiguities are removed that plagued former
approaches with respect to a spin-Hall current that is independent of the
electric field. For the clean Rashba model, the intrinsic spin-Hall
conductivity exhibits a logarithmic divergency in the low-frequency regime.Comment: 19 pages including figure
Hanle effect driven by weak-localization
The influence of weak localization on Hanle effect in a two-dimensional
system with spin-split spectrum is considered. We show that weak localization
drastically changes the dependence of stationary spin polarization
on external magnetic field In particular, the non-analytic dependence of
on is predicted for III-V-based quantum wells grown in
[110] direction and for [100]-grown quantum wells having equal strengths of
Dresselhaus and Bychkov-Rashba spin-orbit coupling. It is shown that in weakly
localized regime the components of are discontinuous at At
low the magnetic field-induced rotation of the stationary polarization is
determined by quantum interference effects. This implies that the Hanle effect
in such systems is totally driven by weak localization.Comment: 4 pages, 1 figur
Controlling the spin orientation of photoexcited electrons by symmetry breaking
We study reflection of optically spin-oriented hot electrons as a means to
probe the semiconductor crystal symmetry and its intimate relation with the
spin-orbit coupling. The symmetry breaking by reflection manifests itself by
tipping the net-spin vector of the photoexcited electrons out of the light
propagation direction. The tipping angle and the pointing direction of the
net-spin vector are set by the crystal-induced spin precession, momentum
alignment and spin-momentum correlation of the initial photoexcited electron
population. We examine non-magnetic semiconductor heterostructures and
semiconductor/ferromagnet systems and show the unique signatures of these
effects.Comment: 4 pages, 3 figures, resubmitte
Spin relaxation of localized electrons in n-type semiconductors
The mechanisms that determine spin relaxation times of localized electrons in
impurity bands of n-type semiconductors are considered theoretically and
compared with available experimental data. The relaxation time of the
non-equilibrium angular momentum is shown to be limited either by hyperfine
interaction, or by spin-orbit interaction in course of exchange-induced spin
diffusion. The energy relaxation time in the spin system is governed by
phonon-assisted hops within pairs of donors with an optimal distance of about 4
Bohr radii. The spin correlation time of the donor-bound electron is determined
either by exchange interaction with other localized electrons, or by spin-flip
scattering of free conduction-band electrons. A possibility of optical cooling
of the spin system of localized electrons is discussed.Comment: Submitted to the special issue "Optical Orientation", Semiconductor
Science and Technolog
Slowing down of spin relaxation in two dimensional systems by quantum interference effects
The effect of weak localization on spin relaxation in a two-dimensional
system with a spin-split spectrum is considered. It is shown that the spin
relaxation slows down due to the interference of electron waves moving along
closed paths in opposite directions. As a result, the averaged electron spin
decays at large times as . It is found that the spin dynamics can be
described by a Boltzmann-type equation, in which the weak localization effects
are taken into account as nonlocal-in-time corrections to the collision
integral. The corrections are expressed via a spin-dependent return
probability. The physical nature of the phenomenon is discussed and it is shown
that the "nonbackscattering" contribution to the weak localization plays an
essential role. It is also demonstrated that the magnetic field, both
transversal and longitudinal, suppresses the power tail in the spin
polarization.Comment: 12 pages, 2 figure
Spin dynamics in the regime of hopping conductivity
We consider spin dynamics in the impurity band of a semiconductor with
spin-split spectrum. Due to the splitting, phonon-assisted hops from one
impurity to another are accompanied by rotation of the electron spin, which
leads to spin relaxation. The system is strongly inhomogeneous because of
exponential variation of hopping times. However, at very small couplings an
electron diffuses over a distance exceeding the characteristic scale of the
inhomogeneity during the time of spin relaxation, so one can introduce an
averaged spin relaxation rate. At larger values of coupling the system is
effectively divided into two subsystems: the one where relaxation is very fast
and another one where relaxation is rather slow. In this case, spin decays due
to escape of the electrons from one subsystem to another. As a result, the spin
dynamics is non-exponential and hardly depends on spin-orbit coupling
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