59 research outputs found
Intrinsic Spin Hall Edges
The prediction of intrinsic spin Hall currents by Murakami \textit{et al.}
and Sinova \textit{et al.} raised many questions about methods of detection and
the effect of disorder. We focus on a contact between a Rashba type spin orbit
coupled region with a normal two-dimensional electron gas and show that the
spin Hall currents, though vanishing in the bulk of the sample, can be
recovered from the edges. We also show that the current induced spin
accumulation in the spin orbit coupled system diffuses into the normal region
and contributes to the spin current in the leads.Comment: To appear in Physical Review Letters. 5 pages, 2 figures, RevTe
Magnetoconductivity in the presence of Bychkov-Rashba spin-orbit interaction
A closed-form analytic formula for the magnetoconductivity in the diffusive
regime is derived in the presence of Bychkov-Rashba spin-orbit interaction in
two dimensions. It is shown that at low fields B << B_{so}, where B_{so} is the
characteristic field associated with spin precession, D'yakonov-Perel'
mechanism leads to spin relaxation, while for B >> B_{so} spin relaxation is
suppressed and the resulting spin precession contributes a Berry phase-like
spin phase to the magnetoconductivity. The relative simplicity of the formula
greatly facilitates data fitting, allowing for the strength of the spin-orbit
coupling to be easily extracted
Rashba spin splitting in biased semiconductor quantum wells
Rashba spin splitting (RSS) in biased semiconductor quantum wells is
investigated theoretically based on the eight-band envelope function model. We
find that at large wave vectors, RSS is both nonmonotonic and anisotropic as a
function of in-plane wave vector, in contrast to the widely used linear and
isotropic model. We derive an analytical expression for RSS, which can
correctly reproduce such nonmonotonic behavior at large wave vectors. We also
investigate numerically the dependence of RSS on the various band parameters
and find that RSS increases with decreasing band gap and subband index,
increasing valence band offset, external electric field, and well width. Our
analytical expression for RSS provides a satisfactory explanation to all these
features.Comment: 5 pages, 4 figures, author names corrected, submitted to Phys. Rev.
Suppression of the Persistent Spin Hall Current by Defect Scattering
We study the linear response spin Hall conductivity of a two-dimensional
electron gas (2DEG) in the presence of the Rashba spin orbit interaction in the
diffusive transport regime. When defect scattering is modeled by isotropic
short-range potential scatterers the spin Hall conductivity vanishes due to the
vertex correction. A non-vanishing spin Hall effect may be recovered for
dominantly forward defect scattering.Comment: Submitted to The Physical Review
Orbital ac spin-Hall effect in the hopping regime
The Rashba and Dresselhaus spin-orbit interactions are both shown to yield
the low temperature spin-Hall effect for strongly localized electrons coupled
to phonons. A frequency-dependent electric field generates a
spin-polarization current, normal to , due to interference of hopping
paths. At zero temperature the corresponding spin-Hall conductivity is real and
is proportional to . At non-zero temperatures the coupling to the
phonons yields an imaginary term proportional to . The interference
also yields persistent spin currents at thermal equilibrium, at .
The contributions from the Dresselhaus and Rashba interactions to the
interference oppose each other.Comment: 4 pages, no figure
Mesoscopic Spin-Hall Effect in 2D electron systems with smooth boundaries
Spin-Hall effect in ballistic 2D electron gas with Rashba-type spin-orbit
coupling and smooth edge confinement is studied. We predict that the interplay
of semiclassical electron motion and quantum dynamics of spins leads to several
distinct features in spin density along the edge that originate from
accumulation of turning points from many classical trajectories. Strong peak is
found near a point of the vanishing of electron Fermi velocity in the lower
spin-split subband. It is followed by a strip of negative spin density that
extends until the crossing of the local Fermi energy with the degeneracy point
where the two spin subbands intersect. Beyond this crossing there is a wide
region of a smooth positive spin density. The total amount of spin accumulated
in each of these features exceeds greatly the net spin across the entire edge.
The features become more pronounced for shallower boundary potentials,
controlled by gating in typical experimental setups.Comment: 4 pages, 4 figures, published versio
Optical Conductivity of a Two-Dimensional Electron Liquid with Spin-Orbit Interaction
The interplay of electron-electron interactions and spin-orbit coupling leads
to a new contribution to the homogeneous optical conductivity of the electron
liquid. The latter is known to be insensitive to many-body effects for a
conventional electron system with parabolic dispersion. The parabolic spectrum
has its origin in the Galilean invariance which is broken by spin-orbit
coupling. This opens up a possibility for the optical conductivity to probe
electron-electron interactions. We analyze the interplay of interactions and
spin-orbit coupling and obtain optical conductivity beyond RPA.Comment: 5 pages, 3 figures; final version, fig. 3 added, minor change
Chiral spin resonance and spin-Hall conductivity in the presence of the electron-electron interactions
We discuss the electron spin resonance in two-dimensional electron gas at
zero external magnetic field. This spin-resonance is due to the transitions
between the electron states, which are split by the spin-orbit (SO)
interaction, and is termed as the chiral spin resonance (CSR). It can be
excited by the in-plane component of the electric field of microwave radiation.
We show that there exists an inherent relationship between the spin-Hall
conductivity and the CSR in a system with the SO interaction. Since in the
presence of the SO interaction spin is not conserved, the electron-electron
interaction renormalizes the spin-Hall conductivity as well as the frequency of
the CSR. The effects of the electron interaction in systems with the SO
interaction are analyzed both phenomenologically and microscopically.Comment: 14 page
Small-angle impurity scattering and the spin Hall conductivity in 2D systems
An arbitrarily small concentration of impurities can affect the spin Hall
conductivity in a two-dimensional semiconductor system. We develop a
Boltzmann-like equation that can be used for impurity scattering with arbitrary
angular dependence, and for arbitrary angular dependence of the spin-orbit
field b(k) around the Fermi surface. For a model applicable to a 2D hole system
in GaAs, if the impurity scattering is not isotropic, we find that the spin
Hall conductivity depends on the derivative of b with respect to the energy and
on deviations from a parabolic band structure, as well as on the angular
dependence of the scattering. In principle, the resulting spin Hall
conductivity can be larger or smaller than the ``intrinsic value'', and can
have opposite sign. In the limit of small angle scattering, in a model
appropriate for small hole concentrations, where the band is parabolic and b ~
k^3, the spin Hall conductivity has opposite sign from the intrinsic value, and
has larger magnitude. Our analysis assumes that the spin-orbit splitting
and the transport scattering rate tau^{-1} are both small compared to the Fermi
energy, but the method is valid for for arbitrary value of b*tau.Comment: Errors corrected, references adde
Out-of-plane spin polarization from in-plane electric and magnetic fields
We show that the joint effect of spin-orbit and magnetic fields leads to a
spin polarization perpendicular to the plane of a two-dimensional electron
system with Rashba spin-orbit coupling and in-plane parallel dc magnetic and
electric fields, for angle-dependent impurity scattering or nonparabolic energy
spectrum, while only in-plane polarization persists for simplified models. We
derive Bloch equations, describing the main features of recent experiments,
including the magnetic field dependence of static and dynamic responses.Comment: 5 pages and 1 figure in main text, 5 pages in appendi
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