1,789 research outputs found
Precessionless spin transport wire confined in quasi-two-dimensional electron systems
We demonstrate that in an inversion-asymmetric two-dimensional electron
system 2DES with both Rashba and Dresselhaus spin-orbit couplings taken into
account, certain transport directions on which no spin precession occurs can be
found when the injected spin is properly polarized. By analyzing the
expectation value of spin with respect to the injected electron state on each
space point in the 2DES, we further show that the adjacent regions with
technically reachable widths along these directions exhibit nearly conserved
spin. Hence a possible application in semiconductor spintronics, namely,
precessionless spin transport wire, is proposed.Comment: 3 pages, 4 figures, to be appeared in Journal of Applied Physics,
Proceedings of the 50th MMM Conferenc
Datta-Das transistor: Significance of channel direction, size-dependence of source contacts, and boundary effects
We analyze the spin expectation values for injected spin-polarized electrons
(spin vectors) in a [001]-grown Rashba-Dresselhaus two-dimensional electron gas
(2DEG). We generalize the calculation for point spin injection in semi-infinite
2DEGs to finite-size spin injection in bounded 2DEGs. Using the obtained spin
vector formula, significance of the channel direction for the Datta-Das
transistor is illustrated. Numerical results indicate that the influence due to
the finite-size injection is moderate, while the channel boundary reflection
may bring unexpected changes. Both effects are concluded to decrease when the
spin-orbit coupling strength is strong. Hence [110] is a robust channel
direction and is therefore the best candidate for the design of the Datta-Das
transistor.Comment: 5 pages, 4 figures, accepted for publication in Physical Review
Local spin density in two-dimensional electron gas with hexagonal boundary
The intrinsic spin-Hall effect in hexagon-shaped samples is investigated. To
take into account the spin-orbit couplings and to fit the hexagon edges, we
derive the triangular version of the tight-binding model for the linear Rashba
[Sov. Phys. Solid State 2, 1109 (1960)] and Dresselhaus [Phys. Rev. 100, 580
(1955)] [001] Hamiltonians, which allow direct application of the
Landauer-Keldysh non-equilibrium Green function formalism to calculating the
local spin density within the hexagonal sample. Focusing on the out-of-plane
component of spin, we obtain the geometry-dependent spin-Hall accumulation
patterns, which are sensitive to not only the sample size, the spin-orbit
coupling strength, the bias strength, but also the lead configurations.
Contrary to the rectangular samples, the accumulation pattern can be very
different in our hexagonal samples. Our present work provides a fundamental
description of the geometry effect on the intrinsic spin-Hall effect, taking
the hexagon as the specific case. Moreover, broken spin-Hall symmetry due to
the coexistence of the Rashba and Dresselhaus couplings is also discussed. Upon
exchanging the two coupling strengths, the accumulation pattern is reversed,
confirming the earlier predicted sign change in spin-Hall conductivity.Comment: 7 pages, 4 figure
Spin precession due to spin-orbit coupling in a two-dimensional electron gas with spin injection via ideal quantum point contact
We present the analytical result of the expectation value of spin resulting
from an injected spin polarized electron into a semi-infinitely extended 2DEG
plane with [001] growth geometry via ideal quantum point contact. Both the
Rashba and Dresselhaus spin-orbit couplings are taken into account. A pictorial
interpretation of the spin precession along certain transport directions is
given. The spin precession due to the Rashba term is found to be especially
interesting since it behaves simply like a windshield wiper which is very
different from the ordinary precession while that due to the Dresselhaus term
is shown to be crystallographic-direction-dependent. Some crystallographic
directions with interesting and handleable behavior of spin precession are
found and may imply certain applicability in spintronic devices.Comment: 5 pages, 2 figures, submitted to Phys. Rev.
Spin and charge transport in U-shaped one-dimensional channels with spin-orbit couplings
A general form of the Hamiltonian for electrons confined to a curved
one-dimensional (1D) channel with spin-orbit coupling (SOC) linear in momentum
is rederived and is applied to a U-shaped channel. Discretizing the derived
continuous 1D Hamiltonian to a tight-binding version, the Landauer-Keldysh
formalism (LKF) for nonequilibrium transport can be applied. Spin transport
through the U-channel based on the LKF is compared with previous quantum
mechanical approaches. The role of a curvature-induced geometric potential
which was previously neglected in the literature of the ring issue is also
revisited. Transport regimes between nonadiabatic, corresponding to weak SOC or
sharp turn, and adiabatic, corresponding to strong SOC or smooth turn, is
discussed. Based on the LKF, interesting charge and spin transport properties
are further revealed. For the charge transport, the interplay between the
Rashba and the linear Dresselhaus (001) SOCs leads to an additional modulation
to the local charge density in the half-ring part of the U-channel, which is
shown to originate from the angle-dependent spin-orbit potential. For the spin
transport, theoretically predicted eigenstates of the Rashba rings, Dresselhaus
rings, and the persistent spin-helix state are numerically tested by the
present quantum transport calculation.Comment: 16 pages, 7 figure
PERCEPTION FIELD FOR A MOBILE DEVICE TO PROVIDE REAL-TIME DEPTH ESTIMATION FOR DETECTED OBJECTS
A mobile computing device (e.g., a mobile phone, camera, tablet computer, wearable and/or headset device) may include an integrated display device (e.g., a presence-sensitive screen) at which a user interface is presented to provide perception field functionality, which enables real-time depth estimation for static or moving objects that are detected by the mobile computing device based on sensory input from an onboard camera. In various examples, this functionality may be embodied in a portable and flexible library (e.g. Android library) that is installed on the mobile computing device. The purpose of perception field monitoring is to provide fast and efficient algorithms for spatial object mapping to enable real-time distance estimation of static and moving objects on a mobile computing device. The implementation of these algorithms may provide spatial location information of targeted objects, as well as distance information associated with objects that are detected by the device. In certain cases, mobile applications executing on the device may utilize such information to provide assistance to visually impaired users by creating audible alerts
Effect Analysis of a Multi-Material Approach to a Problem-Solving Learning System
Abstract-With the rapid development of multimedia, various types of materials used in the design of problemsolving activities have attracted a considerable amount of attention from researchers. The adaptive materials employed in learning activities could enhance learning performance, and motivate learners to seek the solution to a problem. Personalizing a learning environment to optimize individual learning has recently become a popular trend in e-learning. Therefore, this study was carried out to explore how the learning materials of a problem-solving activity influence learning performance; thus we created a multi-material-based learning system (MBLS) consisting of animated game-based material and static text material. The MBLS develops a series of problem-solving tasks to train the learner how to deal with risk. Each task was developed based on the problemsolving model, and the presentation of each task's scenario was classified as either static or dynamic. To achieve the goal of personalized learning, learners could choose the most suitable material for the problem-solving activity. Teachers were included in an expert validation test in this study to examine the performance and reliability of the learning material in the MBLS. The experimental results show that, when the multi-materials are employed, the participants have a 95% probability of obtaining an above-average score using stratification, which suggests that the employed multi-material technique can be a good vehicle for providing adaptive learning that is related to problem solving
Spin-charge conversion in multiterminal Aharonov-Casher ring coupled to precessing ferromagnets: A charge conserving Floquet-nonequilibrium Green function approach
We derive a non-perturbative solution to the Floquet-nonequilibrium Green
function (Floquet-NEGF) describing open quantum systems periodically driven by
an external field of arbitrary strength of frequency. By adopting the
reduced-zone scheme, we obtain expressions rendering conserved charge currents
for any given maximum number of photons, distinguishable from other existed
Floquet-NEGF-based expressions where, less feasible, infinite number of photons
needed to be taken into account to ensure the conservation. To justify our
derived formalism and to investigate spin-charge conversions by spin-orbit
coupling (SOC), we consider the spin-driven setups as reciprocal to the
electric-driven setups in S. Souma et. al., Phys. Rev. B 70, 195346 (2004) and
Phys. Rev. Lett. 94, 106602 (2005). In our setups, pure spin currents are
driven by the magnetization dynamics of a precessing ferromagnetic (FM) island
and then are pumped into the adjacent two- or four-terminal mesoscopic
Aharonov-Casher (AC) ring of Rashba SOC where spin-charge conversions take
place. Our spin-driven results show reciprocal features that excellently agree
with the findings in the electric-driven setups mentioned above. We propose two
types of symmetry operations, under which the AC ring Hamiltonian is invariant,
to argue the relations of the pumped/converted currents in the leads within the
same or between different pumping configurations. The symmetry arguments are
independent of the ring width and the number of open channels in the leads,
terminals, and precessing FM islands, In particular, net pure in-plane spin
currents and pure spin currents can be generated in the leads for certain
setups of two terminals and two precessing FM islands with the current
magnitude and polarization direction tunable by the pumping configuration, gate
voltage covering the two-terminal AC ring in between the FM islands.Comment: Submitted to Physical Review
A Secure and Stable Multicast Overlay Network with Load Balancing for Scalable IPTV Services
The emerging multimedia Internet application IPTV over P2P network preserves significant advantages in scalability. IPTV media content delivered in P2P networks over public Internet still preserves the issues of privacy and intellectual property rights. In this paper, we use SIP protocol to construct a secure application-layer multicast overlay network for IPTV, called SIPTVMON. SIPTVMON can secure all the IPTV media delivery paths against eavesdroppers via elliptic-curve Diffie-Hellman (ECDH) key exchange on SIP signaling and AES encryption. Its load-balancing overlay tree is also optimized from peer heterogeneity and churn of peer joining and leaving to minimize both service degradation and latency. The performance results from large-scale simulations and experiments on different optimization criteria demonstrate SIPTVMON's cost effectiveness in quality of privacy protection, stability from user churn, and good perceptual quality of objective PSNR values for scalable IPTV services over Internet
Current-induced spin polarization in spin-orbit-coupled two-dimensional electron systems
Current-induced spin polarization (CISP) is rederived in ballistic
spin-orbit-coupled electron systems, based on equilibrium statistical
mechanics. A simple and useful picture is correspondingly proposed to help
understand the CISP and predict the polarization direction. Nonequilibrium
Landauer-Keldysh formalism is applied to demonstrate the validity of the
statistical picture, taking the linear Rashba-Dresselhaus [001] two-dimensional
system as a specific example. Spin densities induced by the CISP in
semiconductor heterostructures and in metallic surface states are compared,
showing that the CISP increases with the spin splitting strength and hence
suggesting that the CISP should be more observable on metal and semimetal
surfaces due to the discovered strong Rashba splitting. An application of the
CISP designed to generate a spin-Hall pattern in the inplane, instead of the
out-of-plane, component is also proposed.Comment: 7 pages, 6 figures, 1 table, Phys. Rev. B, in pres
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