Electron Spin Filtering Research Articles

Chiral Pd(II) Nanofiber Promoting Electron Transfer of g-C3N4 for Efficient Photocatalytic Hydrogen Production.

The rapid transfer and separation of photogenerated electrons is very important for the improvement of photocatalytic efficiency. Here, chiral induced spin selectivity effect (CISS effect) was developed to accelerate electron transfer for efficient photocatalytic hydrogen production. A chiral and achiral racemic supramolecular Pd(II) complex nanofiber was fabricated via supramolecular self-assembly of chiral L-Py or its racemes with Pd(II) and used to modify carbon nitride (g-C3N4). The obtained chiral photocatalyst L-Py-Pd/g-C3N4-4 and achiral photocatalyst Rac-Pd/g-C3N4-4, show enhanced photocatalytic activities with hydrogen evolution rates of 2476 and 1339 μmol g-1 h-1, respectively, while that of pure g-C3N4 is 30.5 μmol g-1 h-1. Chiral photocatalyst has 85% higher activity than achiral one and is 82.5-fold of pure g-C3N4, due to better suppression of the recombination of photogenerated electron-hole pairs in the interface of g-C3N4 contact with chiral molecule. Spectral tests and photoelectrochemical tests proved that the chiral supramolecular Pd(II) complex can act both as an electron spin filter and hydrogen reduction catalytic center to enhance photocatalytic efficiency. This work offers a new route to facilitate electron transfer by the CISS effect for photocatalytic hydrogen evolution.

Spin filtering in Dresselhaus spin-orbit-coupled, layered-semiconductor microstructure

Based on Dresselhaus spin-orbit-coupling effect in a layered semiconductor microstructure, an electron-spin filter is proposed. It is found that an obvious spin polarization effect appears and is related to electron energy and in-plane wave vector. It is also found that both magnitude and sign of spin polarization can be controlled by strain engineering or layer's thickness. This layered-semiconductor microstructure can act as a tunable spin filter.

Electron-Spin Filter Based on Dresselhaus Spin-Orbit-Coupling Modulated Single-Layered Semiconductor Nanostructure

We theoretically investigate Dresselhaus spin-orbit coupling (SOC)-induced spin-polarized transport for electrons tunneling through single-layered semiconductor nanostructure (SLSN, InSb). A considerable electron-spin polarization is observed in this SLSN. Spin polarization ratio is associated with the electron energy and in-plane wave vector; in particular, it can be manipulated by the strain engineering or the layer thickness. Based on this SLSN, a controllable electron-spin filter is proposed for spintronics device applications.

Electron-spin polarization effect in Rashba spin-orbit coupling modulated single-layered semiconductor nanostructure

Nanothick semiconductors can grow orderly along a desired direction with the help of modern materials growth technology such as molecular beam epitaxy, which allows researchers to fabricate the so-called layered semiconductor nanostructure (LSN) experimentally. Owing to the structure inversion symmetry broken by the layered form in the LSN, the electron spins interact tightly with its momentums, in the literature referred to as the spin-orbit coupling (SOC) effect, which can be modulated well by the interfacial confining electric field or the stain engineering. These significant SOC effects can effectively eliminate the spin degeneracy of the electrons in semiconductor materials, induce the spin splitting phenomenon at the zero magnetic field and generate the electron-spin polarization in the semiconductors. In recent years, the spin-polarized transport for electrons in the LSN has attracted a lot of research interests, which is because of itself scientific importance and potential serving as spin polarized sources in the research field of semiconductor spintronics. Adopting the theoretical analysis combined with the numerical calculation, we investigate the spin-polarized transport induced by the Rashba-type SOC effect for electrons in a single-layered semiconductor nanostructure (SLSN)-InSb. The present research is to explore the new way of generating and manipulating spin current in semiconductor materials without any magnetic field, and focuses on developing new electron-spin filter for semiconductor spintronics device applications. The improved transfer matrix method (ITMM) is exploited to exactly solve Schrödinger equation for an electron in the SLSN-InSb device, which allows us to calculate the spin-dependent transmission coefficient and the spin polarization ratio. Owing to a strong Rashba-type SOC, a considerable electron-spin polarization effect appears in the SLSN-InSb device. Because of the effective potential experienced by the electrons in the SLSN-InSb device, the spin polarization ratio is associated with the electron energy and the in-plane wave vector. In particular, the spin polarization ratio can be manipulated effectively by an externally-applied electric field or the semiconductor-layer thickness, owing to the dependence of the effective potential felt by the electrons in the SLSN-InSb device on the electric field or the layer thickness. Therefore, such an SLSN-InSb device can be used as a controllable electron-spin filter acting as a manipulable spin-polarized source for the research area of semiconductor spintronics.

Controllable Spin Filtering by δ-Doping for Electrons in Magnetically and Electrically Modulated Semiconductor Nanostructure

In this paper, we theoretically investigate how to control spin filtering via a [Formula: see text]-doping for electrons in a magnetically and electrically modulated semiconductor nanostructure (MEMSN), which can be realized by patterning a ferromagnetic (FM) stripe and a Schottky-metal (SM) stripe on top and bottom of GaAs/AlxGa[Formula: see text]As heterostructure in experiments, respectively. A considerable spin filtering effect still exists because of spin–orbit coupling (SOC), even if a [Formula: see text]-doping is included. Moreover, spin polarization ratio can be manipulated by [Formula: see text]-doping, which may lead to a structurally-controllable electron-spin filter for semiconductor spintronics.

Rashba Spin-Orbit-Coupling Based Electron-Spin Filter in Double-Layered Semiconductor Nanostructure

Based on a double-layered semiconductor nanostructure (DLSN)-InSb/GaSb, we propose a controllable electron-spin filter for spintronics device applications. Electron-spin polarization is induced by Rashba spin-orbit coupling inside the DLSN. Both magnitude and sign of spin polarization ratio can be manipulated by externally-applied electric field or the semiconductor-layer thickness.

Cotrolling electron-spin filter via electric field in layered semiconductor nanostructure

Applying a transverse electric field, we theoretically explore the control of electron-spin filter based on layered semiconductor nanostructure-InSb/InxGa1-xAs. Because of the electric field dependent effective potential of electron, not only size of spin polarization ratio but also its sign can be manipulated by changing magnitude or direction of applied electric field. An electrically-tunable electron-spin filter can be achieved for spintronics device applications.

Spin-orbit-coupling induced electron-spin polarization in magnetically and electrically confined semiconductor microstructure

We theoretically investigate spin polarization for electrons in magnetically and electrically confined semiconductor microstructure, which is constructed by patterning a ferromagnetic stripe and a Schottky-metal stripe on top and bottom of GaAs/AlxGa1-xAs heterostructure, respectively. Both Zeeman interaction and spin–orbit coupling are taken into account; however, electron-spin polarization comes mainly from the latter due to a small effective g-factor for GaAs. Besides, both magnitude and sign of spin polarization can be manipulated by changing interfacial confining electric field or strain engineering, resulting in a tunable electron-spin filter for spintronics device applications.

TUNABLE ELECTRON-SPIN POLARIZATION BY δ-POTENTIAL IN LAYERED SEMICONDUCTOR NANOSTRUCTURE

We theoretically explore how to control electron-spin polarization in layered semiconductor nanostructure (LSN) by a [Formula: see text]-potential realized by atomic-layer doping. Due to Rashba spin-orbit coupling, a considerable spin polarization still remains even through a [Formula: see text]-potential is embedded in the LSN. Spin polarization ratio can be controlled by altering weight or position of [Formula: see text]-potential. Based on such an LSN, a structurally-tunable electron-spin filter may be obtained for spintronics device applications.

Manipulating Electron-Spin Polarization via a δ-Potential in an Embedded Magnetic-Electric-Barrier Microstructure

We theoretically explore how to manipulate electron-spin polarization by a δ-potential in an embedded magnetic-electric-barrier microstructure (EMEBM), which can be fabricated experimentally by patterning a ferromagnetic (FM) stripe and a Schottky-metal (SM) stripe on top and bottom of GaAs/AlxGa1_xAs heterostructure, respectively. Due to spin-orbit coupling (SOC) an appreciable electron-spin polarization effect still remains, even through a δ-potential is contained. Besides, electron-spin polarization ratio can be controlled by δ-potential, which may result in a structurally-manipulable electron-spin filter for spintronics device applications.

Organic Spintronics: A Theoretical Investigation of a Graphene-Porphyrin Based Nanodevice

Spintronics is one of the most exciting applications of graphene-based devices. In this work Density Functional Theory is used to study a nanojunction consisting of two semi-infinite graphene electrodes contacted with an iron-porphyrin (FeP) molecule, which plays the role of spin filter for the incoming unpolarized electrons. The graphene-FeP contact closely resembles the recently synthesized porphyrin-decorated graphene [He et al., Nat. Chem. 2017, 9, 33–38]. The analysis of the spectral properties of the system shows a variation of the orbital occupancy with respect to the isolated FeP molecule and an hybridization with the delocalized states of the substrate, while the overall magnetic moment remains unchanged. Doping the electrodes with boron or nitrogen atoms induces a relevant rearrangement in the electronic structure of the junction. Upon B doping the current becomes significantly spin polarized, while N doping induces a marked Negative Differential Resistivity effect. We have also investigated the possible exploitation of the FeP junction as a gas sensor device. We demonstrate that the interaction of CO and O2 molecules with the Fe atom, while being strong enough to be stable at room temperature (2.0 eV and 1.1 eV, respectively), induces only minor effects on the electronic properties of the junction. Interestingly, a quenching of the spin polarization of the current is observed in the B-doped system.

The Klein Paradox in a Magnetic Field: Effects of Electron Spin

Reflection and transmission of electrons scattered by a rectangular potential step in the presence of an external magnetic field parallel to the electron beam is described with the use of the Dirac equation. It is shown that in addition to the known effects present in the so called Klein paradox, the presence of magnetic field gives rise to electron components with reversed spin in the reflected and transmitted beams. The spin-flip scattering processes are caused by the spin-orbit interaction activated by electric field of the potential step and transverse momentum components of electron motion induced by the magnetic field. The contemporary understanding of the Klein paradox, consisting in the finite transmission even when the potential height tends to infinity, is generalized to the presence of magnetic field and spin-reversed electron beams. The spin-reversed beams are shown to occur also for electrons moving above the step. It is proposed that, accounting for the anomalous value of the electron spin $g$-factor related to radiation corrections, the reflection and transmission scattering from the potential step can be used as an electron spin filter.

Investigation of electron spin dynamic in the bichromatic Kapitza-Dirac effect via frequency ratio and amplitude of laser beams

We discuss electron diffraction from two standing waves with two different frequencies. The effects of increasing the frequency of the second laser beam and changing the laser amplitudes on the form and period of the Rabi oscillation are studied theoretically. The corresponding scattering probabilities for certain incident electron momenta are obtained by an analytical Rabi matrix and numerical solution of the Dirac equation. We show that at high intensities, $\ensuremath{\ge}{10}^{20}$ W ${\mathrm{cm}}^{\ensuremath{-}2}$, the process with an even number of photons involved in the Kapitza-Dirac effect can be used as a spin filter for free electrons. On the other hand, the process with an odd number photons and an electron with momentum along the laser polarization preserves the initial spin of the electron.

Magneto-optical properties of Au upon the injection of hot spin-polarized electrons across Fe/Au(0 0 1) interfaces

We demonstrate a novel method for the excitation of sizable magneto-optical effects in Au by means of the laser-induced injection of hot spin-polarized electrons in Au/Fe/MgO(0 0 1) heterostructures. It is based on the energy- and spin-dependent electron transmittance of Fe/Au interface which acts as a spin filter for non-thermalized electrons optically excited in Fe. We show that after crossing the interface, majority electrons propagate through the Au layer with the velocity on the order of 1 nm fs−1 (close to the Fermi velocity) and the decay length on the order of 100 nm. Featuring ultrafast functionality and requiring no strong external magnetic fields, spin injection results in a distinct magneto-optical response of Au. We develop a formalism based on the phase of the transient complex MOKE response and demonstrate its robustness in a plethora of experimental and theoretical MOKE studies on Au, including our ab initio calculations. Our work introduces a flexible tool to manipulate magneto-optical properties of metals on the femtosecond timescale that holds high potential for active magneto-photonics, plasmonics, and spintronics.

Tunable spin polarization in a δ-doped magnetic-electric-barrier nanostructure

We report a theoretical study on spin filtering of electrons in a hybrid magnetic-electric-barrier (MEB) nanostructure modulated by δ-doping, which can be realized experimentally by depositing a ferromagnetic (FM) stripe and a Schottky-metal (SM) stripe on top of a semiconductor heterostructure and by using atomic-layer doping technique. δ-doping dependent transmission, conductance and spin polarization are calculated by improved transfer matrix method (ITMM) and Landauer–Bűttiker theory (LBT). It elucidates that a spin filtering still exists in MEB device even a δ-doping is comprised inside. Besides, degree of spin filtering can be manipulated by weight or position of δ-doping, which may result in a doping-controllable spin polarized source for spintronics device applications.

Four-photon Kapitza-Dirac effect as an electron spin filter

We theoretically demonstrate the feasibility of producing electron beam splitter using Kapitza-Dirac diffraction on bichromatic standing waves which are created by the fundamental frequency and the third harmonic. The relativistic electron in Bragg regime absorbs three photons with frequency of w and emits a photon with frequency of 3w, four-photon Kapitza-Dirac effect. In this four-photon Kapitza-Dirac effect distinct spin effects arise in different polarizations of the third harmonic laser beam. It is shown that the shape of Rabi oscillation between initial and scattered states is changed and finds two unequal peaks. In circular polarization for fundamental and third harmonic, despite Rabi oscillation, the spin down electron in 0.56 fs intervals maintains its momentum and spin. Also we present an electron spin filter with combination of a linearly polarized fundamental laser beam and a third harmonic with circular polarization that scatters the electron beam according to its spin state.

Spin Filter Based on Magnetically Confined and Spin-Orbit Coupled GaAs/Al<italic>x</italic>Ga1–<italic>x</italic>As Heterostructure

Based on a magnetically confined GaAs/Al x Ga1– x As microstructure modulated by spin-orbit coupling (SOC), we propose a controllable electron-spin filter for spintronics applications. This device operates due to both Zeeman interaction and Rashba or Dresselhaus SOC. Its spin polarization can be tuned by changing interfacial confining electric field or engineering strain.

Electron-spin filter and polarizer in a standing light wave

We demonstrate the theoretical feasibility of spin-dependent diffraction and spin-polarization of an electron in two counter-propagating, circularly polarized laser beams. The spin-dynamics appears in a two-photon process of the Kapitza-Dirac effect in the Bragg regime. We show the spin-dependence of the diffraction process by comparison of the time-evolution of a spin-up and spin-down electron in a relativistic quantum simulation. We further discuss the spin properties of the scattering by studying an analytically approximated solution of the time-evolution matrix. A classification scheme in terms of unitary or non-unitary propagation matrices is used for establishing a generalized and spin-independent description of the spin properties in the diffraction process.

Controlling electron spin dynamics in bichromatic Kapitza-Dirac scattering by the laser field polarization

Spin-dependent Kapitza-Dirac scattering of electron beams from counterpropagating bichromatic laser waves in various polarization geometries is studied. The corresponding scattering probabilities are obtained by analytical and numerical solutions of the time-dependent Dirac equation, assuming a field frequency ratio of 2. When the fundamental field mode is circular-polarized, we show that spin dynamics are generally suppressed at low intensities, but can become distinct at high intensities. Conversely, when a linearly or elliptically polarized fundamental mode is combined with a second harmonic of circular polarization, strong spin effects arise already at low field intensities. In particular, a polarization configuration is identified which acts as a spin filter for free electrons.

A Silicon‐Based Room Temperature Spin Source without Magnetic Layers

Electron spin filtering by DNA on silicon, covalently bound by a 3-isothiocyanatopropyl triethoxy silane linker, provides a means for room temperature spintronics. Electrons from silicon passing through double-stranded DNA acquire a longitudinal spin polarization. This enables the integration of helical molecules as spin filters in modern electronics for spin control, injection, and detection.