563 research outputs found
Spin-dependent tunneling in modulated structures of (Ga,Mn)As
A model of coherent tunneling, which combines multi-orbital tight-binding
approximation with Landauer-B\"uttiker formalism, is developed and applied to
all-semiconductor heterostructures containing (Ga,Mn)As ferromagnetic layers. A
comparison of theoretical predictions and experimental results on
spin-dependent Zener tunneling, tunneling magnetoresistance (TMR), and
anisotropic magnetoresistance (TAMR) is presented. The dependence of spin
current on carrier density, magnetization orientation, strain, voltage bias,
and spacer thickness is examined theoretically in order to optimize device
design and performance.Comment: 9 pages, 13 figures, submitted to PR
Study of Neutron-Rich N = 50 Nuclei
開始ページ、終了ページ: 冊子体のページ付
Direct determination of spin orbit interaction coefficients and realization of the persistent spin helix symmetry
The spin orbit interaction plays a crucial role in diverse fields of
condensed matter, including the investigation of Majorana fermions, topological
insulators, quantum information and spintronics. In III V zinc blende
semiconductor heterostructures, two types of spin orbit interaction, Rashba and
Dresselhaus act on the electron spin as effective magnetic fields with
different directions. They are characterized by coefficients alpha and beta,
respectively. When alpha is equal to beta, the so called persistent spin helix
symmetry is realized. In this condition, invariance with respect to spin
rotations is achieved even in the presence of the spin orbit interaction,
implying strongly enhanced spin lifetimes for spatially periodic spin modes.
Existing methods to evaluate alpha/beta require fitting analyses that often
include ambiguity in the parameters used. Here, we experimentally demonstrate a
simple and fitting parameter free technique to determine alpha/beta and to
deduce the absolute values of alpha and beta. The method is based on the
detection of the effective magnetic field direction and the strength induced by
the two spin orbit interactions. Moreover, we observe the persistent spin helix
symmetry by gate tuning.Comment: 34 pages with 7 figures including supplementary information. appears
in Nature Nanotechnology (2014) Published online 13 July 201
Incommensurate spin correlations induced by magnetic Fe ions substituted into overdoped Bi1.75Pb0.35Sr1.90CuO6+z
Spin correlations in the overdoped region of Bi1.75Pb0.35Sr1.90CuO6+z have
been explored with Fe-doped single crystals characterized by neutron
scattering, muon-spin-rotation (muSR) spectroscopy, and magnetic susceptibility
measurements. Static incommensurate spin correlations induced by the Fe spins
are revealed by elastic neutron scattering. The resultant incommensurability
delta is unexpectedly large (~0.2 r.l.u.), as compared with delta ~ 1/8 in
overdoped superconductor La2-xSrxCuO4. Intriguingly, the large delta in this
overdoped region is close to the hole concentration p. This result is
reminiscent of the delta ~ p trend observed in underdoped La2-xSrxCuO4;
however, it is inconsistent with the saturation of delta in the latter compound
in the overdoped regime. While our findings in Fe-doped
Bi1.75Pb0.35Sr1.90CuO6+z support the commonality of incommensurate spin
correlations in high-Tc cuprate superconductors, they also suggest that the
magnetic response might be dominated by a distinct mechanism in the overdoped
region.Comment: 4 pages, 5 figures. Revision in introduction, discussion, and
conclusion
Downregulation of organic anion transporters in rat kidney under ischemia/reperfusion-induced qacute renal failure
The effect of acute renal failure (ARF) induced by ischemia/reperfusion (I/R) of rat kidney on the expression of organic anion transporters (OATs) was examined. The level of serum indoxyl sulfate (IS), a uremic toxin and substrate of OATs in renal tubules, shows a marked increase with the progression of ARF. However, this increase was significantly attenuated by ingestion of cobalt. The level of mRNA and protein of both rOAT1 and rOAT3 were markedly depressed in the ischemic kidney. The uptake of p-aminohippuric acid (PAH) and estrone sulfate (ES) by renal slices of ischemic rats was significantly reduced compared to control rats. Renal slices taken from ischemic rats treated with cobalt displayed significantly elevated levels of ES uptake. Cobalt intake did not affect PAH uptake, indicating the functional restoration of rOAT3 but not rOAT1. The expression of Na+/K+-ATPase was markedly depressed in the ischemic kidney, suggesting that the inward Na+ gradient in renal tubular cells had collapsed, thereby reducing the outward gradient of α-ketoglutarate, a driving force of both rOATs. The decreased expression of Na+/K+-ATPase was significantly restored by cobalt treatment. Our results suggest that the downregulation of renal rOAT1 and rOAT3 could be responsible for the increase in serum IS level of ischemic rats. Cobalt treatment has a significant protective effect on ischemia-induced ARF, being accompanied by the restoration of rOAT3 and/or Na+/K+-ATPase function
Dynamic nuclear spin polarization in an all-semiconductor spin injection device with (Ga,Mn)As/n-GaAs spin Esaki diode
We investigate the dynamic nuclear spinpolarization in an n-GaAs lateral channel induced by electrical spin injection from a (Ga,Mn)As/n-GaAs spin Esaki diode. Signatures of nuclear spinpolarization are studied in both three-terminal and non-local voltage signals, where a strong electron spin depolarization feature is observed close to zero magnetic field. This is due to the large nuclear field induced in the channel through hyperfine interaction between injected electron spins and localized nuclear spins. We study the time evolution of the dynamic nuclear spinpolarization and evaluate polarization and relaxation times of nuclear spins in the channel
Theory of spin-polarized bipolar transport in magnetic p-n junctions
The interplay between spin and charge transport in electrically and
magnetically inhomogeneous semiconductor systems is investigated theoretically.
In particular, the theory of spin-polarized bipolar transport in magnetic p-n
junctions is formulated, generalizing the classic Shockley model. The theory
assumes that in the depletion layer the nonequilibrium chemical potentials of
spin up and spin down carriers are constant and carrier recombination and spin
relaxation are inhibited. Under the general conditions of an applied bias and
externally injected (source) spin, the model formulates analytically carrier
and spin transport in magnetic p-n junctions at low bias. The evaluation of the
carrier and spin densities at the depletion layer establishes the necessary
boundary conditions for solving the diffusive transport equations in the bulk
regions separately, thus greatly simplifying the problem. The carrier and spin
density and current profiles in the bulk regions are calculated and the I-V
characteristics of the junction are obtained. It is demonstrated that spin
injection through the depletion layer of a magnetic p-n junction is not
possible unless nonequilibrium spin accumulates in the bulk regions--either by
external spin injection or by the application of a large bias. Implications of
the theory for majority spin injection across the depletion layer, minority
spin pumping and spin amplification, giant magnetoresistance, spin-voltaic
effect, biasing electrode spin injection, and magnetic drift in the bulk
regions are discussed in details, and illustrated using the example of a GaAs
based magnetic p-n junction.Comment: 36 pages, 11 figures, 2 table
Novel multi-layer plastic-scintillator-based solid active proton target for inverse-kinematics experiments
We have constructed and tested a novel plastic-scintillator-based solid-state
active proton target for use in nuclear spectroscopic studies with nuclear
reactions induced by an ion beam in inverse kinematics. The active target
system, named Stack Structure Solid organic Scintillator Active Target (S4AT),
consists of five layers of plastic scintillators, each with a 1-mm thickness.
To determine the reaction point in the thickness direction, we exploit the
difference in the energy losses due to the beam particle and the charged
reaction product(s) in the scintillator material. S4AT offers the prospect of a
relatively thick target while maintaining a good energy resolution. By
considering the relative energy loss between different layers, the energy loss
due to unreacted beam particles can be eliminated. Such procedure, made
possible by the multi-layer structure, is essential to eliminate the effect of
unreacted accompanying beam particles, thus enabling its operation at a
moderate beam intensity of up to a few Mcps. We evaluated the performance of
S4AT by measuring the elastic proton-proton scattering using a 70-MeV proton
beam at Cyclotron and Radioisotope Center (CYRIC), Tohoku University.Comment: 32 pages, 14 figure
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