4,507 research outputs found
Mesoscopic Spin Hall Effect in Multiprobe Ballistic Spin-Orbit Coupled Semiconductor Bridges
We predict that unpolarized charge current driven through the longitudinal
leads attached to ballistic quantum-coherent two-dimensional electron gas
(2DEG) in semiconductor heterostructure will induce a {\em pure} spin current,
which is not accompanied by any net charge flow, in the transverse voltage
probes. Its magnitude can be tuned by the Rashba spin-orbit (SO) interaction
and, moreover, it is resilient to weak spin-independent scattering off
impurities within the metallic diffusive regime. While the polarization vector
of the spin transported through the transverse leads is not orthogonal to the
plane of 2DEG, we demonstrate that only two components (out-of-plane and
longitudinal) of the transverse spin current are signatures of the spin Hall
effect in four-probe Rashba spin-split semiconductor nanostructures. The linear
response spin Hall current, obtained from the multiprobe Landauer-B\" uttiker
scattering formalism generalized for quantum transport of spin, is the
Fermi-surface determined nonequilibrium quantity whose scaling with the 2DEG
size reveals the importance of processes occurring on the spin precession
{\em mesoscale} (on which spin precesses by an angle )--the
out-of-plane component of the transverse spin current exhibits quasioscillatory
behavior for (attaining the maximum value in 2DEGs of
the size ), while it reaches the asymptotic value
in the macroscopic regime . Furthermore, these values of the
spin Hall current can be manipulated by the measuring geometry defined by the
attached leads.Comment: 12 pages, 6 color EPS figures; expanded discussion to emphasize
crucial role played by processes on the spin precession mesoscal
An association between pulmonary Mycobacterium avium-intracellulare complex infections and biomarkers of Th2-type inflammation
Background: The rising incidence of pulmonary Mycobacterium avium-intracellulare complex (MAI) infection is unexplained but parallels the growing world-wide epidemic of allergic disease. We hypothesized an association between pulmonary MAI infection and Th2-type immune responses as seen in allergy. / Methods: Biomarkers of patient Th2-type immune responses (peripheral blood eosinophil counts and serum IgE levels) were compared between patients with positive pulmonary samples for tuberculosis and non-tuberculous mycobacterial (NTM) infection. A further comparison of clinical characteristics, including respiratory co-morbidities, and biomarkers, was conducted between patients culturing MAI NTM and those culturing NTM other than MAI. / Results: Patients culturing NTM from pulmonary samples had significantly higher peripheral blood eosinophil levels than those culturing Mycobacterium tuberculosis. Furthermore, patients culturing MAI compared to those culturing NTM other than MAI had higher eosinophil counts (mean 0.29x109/L vs 0.15x109/L, p=0.010) and IgE levels (geometric mean 138kU/L vs 47kU/L, p=0.021). However there was no significant difference in the frequency of asthma between the two NTM groups. / Conclusions: There is an association between biomarkers of Th2-type immune responses and pulmonary MAI. Prospective and translational research could identify the direction of causation; and so determine whether our finding may be utilized within future management strategies for MAI
Temperature dependence of the electron spin g factor in GaAs
The temperature dependence of the electron spin factor in GaAs is
investigated experimentally and theoretically. Experimentally, the factor
was measured using time-resolved Faraday rotation due to Larmor precession of
electron spins in the temperature range between 4.5 K and 190 K. The experiment
shows an almost linear increase of the value with the temperature. This
result is in good agreement with other measurements based on photoluminescence
quantum beats and time-resolved Kerr rotation up to room temperature. The
experimental data are described theoretically taking into account a diminishing
fundamental energy gap in GaAs due to lattice thermal dilatation and
nonparabolicity of the conduction band calculated using a five-level kp model.
At higher temperatures electrons populate higher Landau levels and the average
factor is obtained from a summation over many levels. A very good
description of the experimental data is obtained indicating that the observed
increase of the spin factor with the temperature is predominantly due to
band's nonparabolicity.Comment: 6 pages 4 figure
On the environmental decoherence and spin interference in mesoscopic loop structures
Mechanisms of 'environmental decoherence' such as surface scattering,
Elliot-Yafet process and precession mechanisms, as well as their influence on
the spin phase relaxation are considered and compared. It is shown that the
'spin ballistic' regime is possible, when the phase relaxation length for the
spin part of the wave function (WF)is much greater than the phase relaxation
length for the 'orbital part'. In the presence of an additional magnetic field,
the spin part of the electron's WF acquires a phase shift due to additional
spin precession about that field. If the structure length is chosen to be
greater than the phase relaxation length for the 'orbital part' and less than
the phase relaxation length for the spin part of WF, it is possible to 'wash
out' the quantum interference related to the phase coherence of the 'orbital
part' of the WF, retaining at the same time that related to the phase coherence
of the spin part and, hence, to reveal corresponding conductance oscillations
Combined effect of Zeeman splitting and spin-orbit interaction on the Josephson current in a S-2DEG-S structure
We analyze new spin effects in current-carrying state of superconductor-2D
electron gas-superconductor (S-2DEG-S) device with spin-polarized nuclei in
2DEG region. The hyperfine interaction of 2D electrons with nuclear spins,
described by the effective magnetic field B, produces Zeeman splitting of
Andreev levels without orbital effects, that leads to the interference pattern
of supercurrent oscillations over B. The spin-orbit effects in 2DEG cause
strongly anisotropic dependence of the Josephson current on the direction of B,
which may be used as a probe for the spin-orbit interaction intensity. Under
certain conditions, the system reveals the properties of pi-junction.Comment: 4 pages, 4 figure
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