417 research outputs found
Spin and transport effects in quantum microcavities with polarization splitting
Transport properties of exciton-polaritons in anisotropic quantum
microcavities are considered theoretically. Microscopic symmetry of the
structure is taken into account by allowing for both the
longitudinal-transverse (TE-TM) and anisotropic splitting of polariton states.
The splitting is equivalent to an effective magnetic field acting on polariton
pseudospin, and polarization conversion in microcavities is shown to be caused
by an interplay of exciton-polariton spin precession and elastic scattering. In
addition, we considered the spin-dependent interference of polaritons leading
to weak localization and calculated coherent backscattering intensities in
different polarizations. Our findings are in a very good agreement with the
recent experimental data.Comment: 8 pages, 6 figure
Magnetotransport in disordered delta-doped heterostructures
We discuss theoretically how electrons confined to two dimensions in a
delta-doped heterostructure can arrange themselves in a droplet-like spatial
distribution due to disorder and screening effects when their density is low.
We apply this droplet picture to magnetotransport and derive the expected
dependence on electron density of several quantities relevant to this
transport, in the regimes of weak and moderate magnetic fields. We find good
qualitative and quantitative agreement between our calculations and recent
experiments on delta-doped heterostructures.Comment: 10 pages RevTeX, 2 figures, uses psfrag; published versio
Imaging spin flows in semiconductors subject to electric, magnetic, and strain fields
Using scanning Kerr microscopy, we directly acquire two-dimensional images of
spin-polarized electrons flowing laterally in bulk epilayers of n:GaAs. Optical
injection provides a local dc source of polarized electrons, whose subsequent
drift and/or diffusion is controlled with electric, magnetic, and - in
particular - strain fields. Spin precession induced by controlled uniaxial
stress along the axes demonstrates the direct k-linear spin-orbit
coupling of electron spin to the shear (off-diagonal) components of the strain
tensor.Comment: 5 pages, 5 color figure
Slow imbalance relaxation and thermoelectric transport in graphene
We compute the electronic component of the thermal conductivity (TC) and the
thermoelectric power (TEP) of monolayer graphene, within the hydrodynamic
regime, taking into account the slow rate of carrier population imbalance
relaxation. Interband electron-hole generation and recombination processes are
inefficient due to the non-decaying nature of the relativistic energy spectrum.
As a result, a population imbalance of the conduction and valence bands is
generically induced upon the application of a thermal gradient. We show that
the thermoelectric response of a graphene monolayer depends upon the ratio of
the sample length to an intrinsic length scale l_Q, set by the imbalance
relaxation rate. At the same time, we incorporate the crucial influence of the
metallic contacts required for the thermopower measurement (under open circuit
boundary conditions), since carrier exchange with the contacts also relaxes the
imbalance. These effects are especially pronounced for clean graphene, where
the thermoelectric transport is limited exclusively by intercarrier collisions.
For specimens shorter than l_Q, the population imbalance extends throughout the
sample; the TC and TEP asymptote toward their zero imbalance relaxation limits.
In the opposite limit of a graphene slab longer than l_Q, at non-zero doping
the TC and TEP approach intrinsic values characteristic of the infinite
imbalance relaxation limit. Samples of intermediate (long) length in the doped
(undoped) case are predicted to exhibit an inhomogeneous temperature profile,
whilst the TC and TEP grow linearly with the system size. In all cases except
for the shortest devices, we develop a picture of bulk electron and hole number
currents that flow between thermally conductive leads, where steady-state
recombination and generation processes relax the accumulating imbalance.Comment: 14 pages, 4 figure
Direct measurement of a pure spin current by a polarized light beam
The photon helicity may be mapped to a spin-1/2, whereby we put forward an
intrinsic interaction between a polarized light beam as a ``photon spin
current'' and a pure spin current in a semiconductor, which arises from the
spin-orbit coupling in valence bands as a pure relativity effect without
involving the Rashba or the Dresselhaus effect due to inversion asymmetries.
The interaction leads to circular optical birefringence, which is similar to
the Faraday rotation in magneto-optics but nevertheless involve no net
magnetization. The birefringence effect provide a direct, non-demolition
measurement of pure spin currents.Comment: Erratum version to [Physical Review Letter 100, 086603 (2008)
Numerical study of resonant spin relaxation in quasi-1D channels
Recent experiments demonstrate that a ballistic version of spin resonance,
mediated by spin-orbit interaction, can be induced in narrow channels of a
high-mobility GaAs two-dimensional electron gas by matching the spin precession
frequency with the frequency of bouncing trajectories in the channel. Contrary
to the typical suppression of Dyakonov-Perel' spin relaxation in confined
geometries, the spin relaxation rate increases by orders of magnitude on
resonance. Here, we present Monte Carlo simulations of this effect to explore
the roles of varying degrees of disorder and strength of spin-orbit
interaction. These simulations help to extract quantitative spin-orbit
parameters from experimental measurements of ballistic spin resonance, and may
guide the development of future spintronic devices
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