9 research outputs found
Spin relaxation in the impurity band of a semiconductor in the external magnetic field
Spin relaxation in the impurity band of a 2D semiconductor with spin-split
spectrum in the external magnetic field is considered. Several mechanisms of
spin relaxation are shown to be relevant. The first one is attributed to
phonon-assisted transitions between Zeeman sublevels of the ground state of an
isolated impurity, while other mechanisms can be described in terms of spin
precession in a random magnetic field during the electron motion over the
impurity band. In the later case there are two contributions to the spin
relaxation: the one given by optimal impurity configurations with the
hop-waiting time inversely proportional to the external magnetic field and
another one related to the electron motion on a large scale. The average spin
relaxation rate is calculated
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
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
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 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
Electron density stratification in two-dimensional structures tuned by electric field
A new kinetic instability which results in formation of charge density waves
is proposed. The instability is of a purely classical nature. A spatial period
of arising space-charge and field configuration is inversely proportional to
electric field and can be tuned by applied voltage. The instability has no
interpretation in the framework of traditional hydrodynamic approach, since it
arises from modulation of an electron distribution function both in coordinate
and energy spaces. The phenomenon can be observed in thin 2D nanostructures at
relatively low electron density.Comment: 4 pages, 2 figure