Lateral Shifts for Spin Electrons in a Hybrid Magnetic-Electric-Barrier Nanostructure Modulated by Spin-Orbit Couplings

We theoretically investigate how to modulate spin-dependent lateral shifts by the spin-orbit coupling (SOC) in a hybrid magnetic-electric-barrier (MEB) nanostructure, which can be experimentally realized by depositing a ferromagnetic (FM) stripe and a Schottky metal (SM) stripe on the top and bottom of the semiconductor heterostructure, respectively. Two kinds of ROCs, Rashba SOC (RSOC) and Dresselhaus SOC (DSOC), are taken into account fully. The Schrödinger equation of the spin electron in the hybrid MEB nanostructure is exactly solved by using the improved transfer-matrix method (ITMM), and the lateral shift and its spin polarization are numerically calculated with the help of the stationary phase method (SPM). Theoretical analysis indicates that the spin polarization effect in the lateral shift still exists in the hybrid MEB nanostructure when the SOCs are considered. Numerical simulations show that both magnitude and sign of the spin polarization effect in lateral shifts vary strongly with the strengths of RSOC and DSOC. These interesting features may offer an effective means to control the behavior of spin-polarized electrons in the semiconductor nanostructure, and such a hybrid MEB nanostructure serves as a SOC-manipulable spatial spin splitter for spintronic applications.     

Manipulating Transmission of a Two-Dimensional Electron Gas Modulated by Ferromagnetic and Schottky Metal Stripes

We study how the transmission properties of a two-dimensional electron gas, modulated by a ferromagnetic stripe and a Schottky metal (SM) stripe in a parallel configuration, can be modified by manipulating the voltage applied to the SM stripe. Both the transmission coefficient and conductance of the device are found to be strongly dependent on the electric-barrier height induced by an applied voltage under the SM stripe. Thus, transmission properties of electrons in the device can be conveniently tailored by means of tuning this applied voltage.     

Enhancement of spin polarization in a transition metal oxide ferromagnetic nanodot diode

Enhancement of spin polarization was observed in a transition metal oxide (Fe,Zn)(3)O(4)/Nb-SrTiO(3) ferromagnetic nanodot Schottky diode. The highly integrated oxide nanodot diodes were constructed using nanoimprint lithography based on a Mo lift-off method in combination with a pulsed laser deposition technique. The junction magnetoresistance of diodes increased as diode size increased. The spin polarization estimated from the thermionic emission model is enhanced from P = 0.74 in a conventional film to P = 0.89 in a nanodot diode whose size is 300 × 300 nm(2). The nanofabrication technique used here will enable us to construct superior transition metal oxide spintronic nanomaterial and nanodevices.     

Spin injection in spin FETs using a step-doping profile

We investigate the effect of a step-doping profile on the spin injection from a ferromagnetic metal contact into a semiconductor quantum well in spin field-effect transistors using a Monte Carlo model. The considered scheme uses a heavily doped layer at the metal-semiconductor interface to vary the Schottky barrier shape and enhance the tunneling current. It is found that spin flux (spin current density) is enhanced proportionally to the total current, and the variation of current spin polarization does not exceed 20%.     

Effect of Ferromagnetic Metal Stripe and Strained Barrier on Electron Transport Characteristics in a Graphene

In this paper, the effect of ferromagnetic metal stripe and the strained barrier on the valley-dependent transport characteristics of electrons is studied in a graphene nanostructure. The numerical results show that a large valley polarization can be obtained in such a graphene, and the valley-dependent transport characteristics can be well controlled by changing the strength of the magnetic field induced by the ferromagnetic metal stripe, the width of the ferromagnetic metal stripe and the position of the strained barrier. Therefore, the valley polarization can be modulated by controlling the ferromagnetic metal stripe and the strained barrier. This work can promote the research and development of the new valleytronic devices, and then meet the practical application needs.

     

Switching of Current Spin Polarization by Electron-Phonon Interaction in a Quantum Dot Device

We study spin-polarized electron transport through a quantum dot coupled to one normal metal lead and one ferromagnetic lead. Both the intradot Coulomb correlation and the electron-phonon interaction are taken into account in the framework of nonequilibrium Green’s function theory. We find that due to the interplay of the Coulomb blockade effect and the phonon-induced extra electron transport channels, the spin polarization of the electron current driven by external bias voltage is enhanced in a range of negative biases in which the current is flowing from the ferromagnetic lead to the normal metal one. While for the corresponding positive biases, the current polarization is suppressed to negative values where the current is flowing from the normal metal lead to the ferromagnetic one. The device thus operates as a current polarization switcher without the need of a magnetic field or spin-orbit interaction, and may find use in low-power spintronic devices with the help of phonon engineering techniques.     

The Hanle effect and electron spin polarization in InAs/GaAs quantum dots up to room temperature

The Hanle effect in InAs/GaAs quantum dots (QDs) is studied under optical orientation as a function of temperature over the range of 150-300 K, with the aim of understanding the physical mechanism responsible for the observed sharp increase of electron spin polarization with increasing temperature. The deduced spin lifetime T(s) of positive trions in the QDs is found to be independent of temperature, and is also insensitive to excitation energy and density. It is argued that the measured T(s) is mainly determined by the longitudinal spin-flip time (T(1)) and the spin dephasing time (T(2)*) of the studied QD ensemble, of which both are temperature independent over the studied temperature range and the latter makes a larger contribution. The observed sharply rising QD spin polarization degree with increasing temperature, on the other hand, is shown to be induced by an increase in spin injection efficiency from the barrier/wetting layer and also by a moderate increase in spin detection efficiency of the QD.     

Analysis of Response Functions of a Spin-Polarized Electron Gas

We present a spin analysis of local-field corrections and various susceptibility functions of a spin-polarized electron gas (SPEG). With a use of spin-resolved pair correlation functions of the SPEG, including the carrier correlations, we evaluate the local-field correction within a generalized random-phase approximation (RPA) and examine spin-polarization dependences of various susceptibility functions generalized in terms of spin-dependent local-field corrections. A pronounced maximum in spin-resolved local-field correction is observed and the location of the peaks are found to depend strongly on the values of spin polarization. For a system with vanishing spin polarization, the charge–spin mixed susceptibilities vanish. However, in the SPEG of finite spin polarization, the mixed susceptibilities become finite and are as important as the usual charge–charge, and spin–spin susceptibilities.     

DNA Molecule as a Spintronic Device

In this work, we study the spin-dependent electron transport of a segment of DNA chain. We model the system by using the Fishbone model for DNA, which is characterized by a tight binding Hamiltonian. We predict that the spin-dependent transport can be observed in short DNA molecules coupled to metal contacts by applying an external magnetic field. A detailed analysis of spin-dependent current and spin polarization as a function of the bias voltages is carried out.     

Proximity-effect correction in electron-beam lithography on metal multi-layers

We report a proximity-effect correction in electron beam patterning when fabricating a spin valve device with a junction size of 100 nm × 100 nm. Since the spin valve device has a stack of magnetic/non-magnetic/magnetic metal multi-layers on oxidized Si substrate, its proximity effect should be appropriately corrected to realize a nano-scale junction. ZEP 520A was chosen as an electron beam resist because its dry-etching resistance is high enough to serve as an etching mask in the post-process. A set of proximity parameters, α, β, and η of ZEP 520A coated metal multi-layers was evaluated by using the doughnut pattern method. A simulation was carried out based on given proximity parameters in order to obtain effective dose factors of each segment of the exposure pattern. The junction with a desired shape and size on a metal multi-layer was successfully fabricated with a help of efficient proximity-effect correction.     

Ballistic electron transport in a nanostructure under the influence of magnetic barriers and δ-doping

The electron transport properties are theoretically investigated in a nanostructure under the influence of magnetic barriers and the δ-doping. The resulting transmission and spin polarization are strongly dependent on the weight of δ-doping. It is shown that the large spin polarization can be achieved due to the remarkable discrepancy in the transmission for electrons with opposite spin orientations. It is also shown that both the transmission probability and the spin polarization periodically change with the increase of L. These interesting features will be more helpful for developing new types of spintronic devices.     

Ballistic electron transport in a nanostructure under the influence of magnetic barriers and δ-doping

The electron transport properties are theoretically investigated in a nanostructure under the influence of magnetic barriers and the δ-doping. The resulting transmission and spin polarization are strongly dependent on the weight of δ-doping. It is shown that the large spin polarization can be achieved due to the remarkable discrepancy in the transmission for electrons with opposite spin orientations. It is also shown that both the transmission probability and the spin polarization periodically change with the increase of L. These interesting features will be more helpful for developing new types of spintronic devices.     

Binocular imaging of a laser stripe and approximation networks for shape detection

A technique for shape detection based on binocular imaging of a laser stripe is presented. In this technique, the object shape is recovered by means of laser stripe projection and binocular imaging. The approach of the binocular imaging in this technique is to avoid stripe occlusions, which appear due to the variation to the object surface. Based on the behavior of the stripe displacement, the object topography is computed by a Bezier approximation network. By means of this network, the measurements of the binocular geometry are avoided. The parameters of the binocular imaging are computed based on the Bezier approximation network. To reconstruct the topography, the object is scanned by a laser stripe. From the scanning, a set of binocular images of the stripe are processed to compute the object dimensions by means of the network. By applying Bezier approximation networks, the performance of the binocular imaging and the accuracy are improved. It is because the errors of the measurement are not added to the computational procedure, which performs the shape reconstruction. This procedure represents a contribution for the stripe projection methods and the binocular imaging. To describe the accuracy a root mean square of error is calculated. This technique is tested with real objects and its experimental results are presented. Also, the time processing is described. © 2007 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 17, 62–74, 2007     

Electrical Spin Injection in a Ferromagnetic Metal/Insulator/Semiconductor Tunnel Heterostructure

We demonstrate experimentally the electrical spin injection from a ferromagnetic metal/tunnel barrier contact into a semiconductor III–V heterostructure. The injected electrons have an in-plane spin orientation. We show that by applying an oblique external magnetic field this spin orientation can be manipulated within the semiconductor, and a nonzero perpendicular spin component arises. This perpendicular component can be easily monitored by optical means (circular polarization of the emitted light). In a CoFe/AlO _x /(Al,Ga)As/GaAs heterostructure we observe injected spin polarization in access of 9% at 80 K and optimized structures have recently shown spin injection up to room temperature.     

Electrical Electron Spin Injection with a p+-(Ga,Mn)As/n+-GaAs Tunnel Junction

We demonstrate electrical electron spin injection in a p⁺-(Ga,Mn)As/n⁺-GaAs tunnel junction with an n-GaAs/(In,Ga)As/p-GaAs light emitting diode (LED). By applying a reverse bias to the p⁺-(Ga,Mn)As/n⁺-GaAs junction (forward bias to the LED), we observed clear hysteresis in electroluminescence (EL) polarization. The magnitude of the EL polarization, which does not depend critically on the spacer layer thickness up to 800 nm, is found to be about five times greater than that of the hole spin injection.     

Electric stability of spatiotemporal stripe patterns formed by silver and antimony co-electrodeposition under the constant current mode

During Ag/Sb (silver and antimony) co-electrodeposition, various spatiotemporal patterns, which are similar to those in the reaction–diffusion system, are observed on the metal electrode surface. In our previous paper, we reported the phase diagram of several kinds of propagating stripe patterns as a function of constant current density, using an optical microscope. For several phases in the phase diagram, we discovered that the spatial bifurcation to two dynamic stripe patterns took place on the electrode surface at the initial stage of electrodeposition, and eventually, these two patterns transferred into one of the patterns in time. In this study, in order to compare the electric stability of such patterns, the potential time-evolution of each phase, in which the spatial bifurcation of patterns occurs, was investigated. From the experimental results, it was found that the patterns each have an inherent range or value of potential at which they are formed. However, the potential did not necessarily reach the value with low electric energy. Namely, this finding indicates that various other factors contribute to this phenomenon in addition to the electric stability.     

Unique vortex and stripe domain structures in PbTiO3 epitaxial nanodots

The domain structures of PbTiO₃ epitaxial nanodots under the influences of depolarization fields and mismatch strains have been studied using three dimensional phase field simulations. The single-vortex structure and mixed domain configuration, which consisted of zigzag stripe domain and closure dipole flux near the interfaces, were found to be effective in annihilating the depolarization fields in the isotropically tensile and compressive ferroelectric nanodots, respectively. These domain structures were produced by the combined effect of electrostatic and mismatch elastic energies. The width of stripe domain was found to be related to the volume percentage of polarization dipoles along the z-axis, which varied remarkably with the change of compressive mismatch strain. In the case of nanodots under anisotropic mismatch strains, double-vortex domain patterns and stripe domains with nearly straight domain walls were formed. Moreover, the domain structures with electrostatic energy neglected were also studied.     

Electrical Electron Spin Injection with a p+-(Ga,Mn)As/n+-GaAs Tunnel Junction

We demonstrate electrical electron spin injection in a p⁺-(Ga,Mn)As/n⁺-GaAs tunnel junction with an n-GaAs/(In,Ga)As/p-GaAs light emitting diode (LED). By applying a reverse bias to the p⁺-(Ga,Mn)As/n⁺-GaAs junction (forward bias to the LED), we observed clear hysteresis in electroluminescence (EL) polarization. The magnitude of the EL polarization, which does not depend critically on the spacer layer thickness up to 800 nm, is found to be about five times greater than that of the hole spin injection.     

Stability of parallel stripe domains

The stability of a periodic array of parallel stripe domains in LPE garnet films is investigate both theoretically and experimentally. The vehicle used is the confined region of the bubble lattice device [1] which allows the initialization of straight parallel stripes as well as allowing a variation in the period of the stripe domains. The domains are analyzed wlth respect to the stable number of straight parallel stripes for a given bias field and to their stability with respect to sinusoidal distortions (buckling). The results show that a stable range of bias exists between the upper limit of stripe contraction and the lower limit of stripe buckling.     

Nanocrystal shape and the mechanism of exciton spin relaxation

The rate of exciton spin relaxation (flips) between the bright exciton states (F = +/-1) of CdSe nanocrystals is reported as a function of shape, for dots and nanorods. The spin relaxation is measured using an ultrafast transient grating method with a crossed linearly polarization sequence. It is found that the spin relaxation rate depends on the radius, not length, of the nanocrystals. That observation is explained by deriving an expression for the electronic coupling matrix element that mixes the bright exciton states.