410 research outputs found
Magnetoresistance due to edge spin accumulation
Because of spin-orbit interaction, an electrical current is accompanied by a
spin current resulting in spin accumulation near the sample edges. Due again to
spin-orbit interaction this causes a small decrease of the sample resistance.
An applied magnetic field will destroy the edge spin polarization leading to a
positive magnetoresistance. This effect provides means to study spin
accumulation by electrical measurements. The origin and the general properties
of the phenomenological equations describing coupling between charge and spin
currents are also discussed.Comment: 4 pages, 3 figures. Minor corrections corresponding to the published
versio
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
Bremsstrahlung Spectrum in alpha Decay
Using our previous approach to electromagnetic emission during tunneling, an
explicit, essentially classical, formula describing the bremsstrahlung spectrum
in alpha decay is derived. The role of tunneling motion in photon emission is
discussed. The shape of the spectrum is a universal function of the ratio Eg/Eo
, where Eg is the photon energy and Eo is a characteristic energy depending
only on the nuclear charge and the energy of the alpha particle.Comment: 8 pages, 3 figure
Geometrical phase effects on the Wigner distribution of Bloch electrons
We investigate the dynamics of Bloch electrons using a density operator
method and connect this approach with previous theories based on wave packets.
We study non-interacting systems with negligible disorder and strong spin-orbit
interactions, which have been at the forefront of recent research on
spin-related phenomena. We demonstrate that the requirement of gauge invariance
results in a shift in the position at which the Wigner function of Bloch
electrons is evaluated. The present formalism also yields the correction to the
carrier velocity arising from the Berry phase. The gauge-dependent shift in
carrier position and the Berry phase correction to the carrier velocity
naturally appear in the charge and current density distributions. In the
context of spin transport we show that the spin velocity may be defined in such
a way as to enable spin dynamics to be treated on the same footing as charge
dynamics. Aside from the gauge-dependent position shift we find additional,
gauge-covariant multipole terms in the density distributions of spin, spin
current and spin torque.Comment: 12 pages, 3 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
Spin dynamics of two-dimensional electrons with Rashba spin-orbit coupling and electron-electron interactions
We study the spin dynamics of two dimensional electron gases (2DEGs) with
Rashba spin-orbit coupling by taking account of electron-electron interactions.
The diffusion equations for charge and spin densities are derived by making use
of the path-integral approach and the quasiclassical Green's function.
Analyzing the effect of the interactions, we show that the spin-relaxation time
can be enhanced by the electron-electron interaction in the ballistic regime.Comment: accepted for publication in Phys. Rev.
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
Exciton spin decay modified by strong electron-hole exchange interaction
We study exciton spin decay in the regime of strong electron-hole exchange
interaction. In this regime the electron spin precession is restricted within a
sector formed by the external magnetic field and the effective exchange fields
triggered by random spin flips of the hole. Using Hanle effect measurements, we
demonstrate that this mechanism dominates our experiments in CdTe/(Cd,Mg)Te
quantum wells. The calculations provide a consistent description of the
experimental results, which is supported by independent measurements of the
parameters entering the model.Comment: 5 pages, 3 figure
Dependence of the intrinsic spin Hall effect on spin-orbit interaction character
We report on a comparative numerical study of the spin Hall conductivity in
two-dimensions for three different spin-orbit interaction models; the standard
k-linear Rashba model, the k-cubic Rashba model that describes two-dimensional
hole systems, and a modified k-linear Rashba model in which the spin-orbit
coupling strength is energy dependent. Numerical finite-size Kubo formula
results indicate that the spin Hall conductivity of the k-linear Rashba model
vanishes for frequency much smaller than the scattering rate
, with order one relative fluctuations surviving out to large system
sizes. For the k-cubic Rashba model case, the spin Hall conductivity does not
depend noticeably on and is finite in the {\em dc} limit, in
agreement with experiment. For the modified k-linear Rashba model the spin Hall
conductivity is noticeably dependent but approaches a finite
value in the {\em dc} limit. We discuss these results in the light of a
spectral decomposition of the spin Hall conductivity and associated sum rules,
and in relation to a proposed separation of the spin Hall conductivity into
skew-scattering, intrinsic, and interband vertex correction contributions.Comment: 10 pages, 4 figure
Interference induced metallic-like behavior of a two-dimensional hole gas in asymmetric GaAs/InGaAs/GaAs quantum well
The temperature and magnetic field dependences of the conductivity of the
heterostructures with asymmetric InGaAs quantum well are studied.
It is shown that the metallic-like temperature dependence of the conductivity
observed in the structures investigated is quantitatively understandable within
the whole temperature range, K. It is caused by the interference
quantum correction at fast spin relaxation for 0.4 K K. At higher
temperatures, 1.5 K K, it is due to the interaction quantum correction.
Finally, at K, the metallic-like behavior is determined by the phonon
scattering.Comment: 4 pages, 4 figure
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