Spin Direction Of Electrons Research Articles

Elimination of zero-field splitting frequency drift of nitrogen vacancy center ensembles in diamond induced by temperature noise

The electron spin state of the NV color center in the diamond is optically polarized and read out by laser. However, laser irradiation introduces additional temperature noise, and the zero-field splitting term in the Hamiltonian becomes unstable. The main objective of this study is to explain and eliminate the influence of temperature noise generated by laser power and to propose a laser pulse shaping for detection. Experimental results show that the additional −2.8 MHz frequency drift introduced by the high-power laser is suppressed, under the condition of achieving the same resonance peak contrast of the high-power laser.

Anomalous Laser-Fluence Dependence of Electron Spin Excitation in CdS Colloidal Quantum Dots: Surface Effects.

Electron spin dynamics in CdS quantum dots (QDs) with hole acceptor 1-octanethiol organic molecules are investigated by time-resolved ellipticity spectroscopy. An anomalous dependence of laser fluences on electron spin excitation for the first time is reported. Increasing the laser fluence, the electron spin is switched from one direction to an antiparallel direction (spin direction switching, SDS) when adding enough 1-octanethiol hole acceptors in an air atmosphere. The analysis shows that the electron spin direction changes from heavy hole excitation defined to spin-orbit split hole excitation defined. In as-grown CdS QDs with native ligands, laser-fluence-dependent SDS phenomena are absent. Electron wave function spread into 1-octanethiol molecules is demonstrated to be important for the presence of SDS phenomena. The finding here thus reveals the importance of surface conditions on electron spin excitation processes in semiconductor QDs and that the surface can be used as an important factor to manipulate the spin.

Examining the Effects of Homochirality for Electron Transfer in Protein Assemblies.

Protein voltammetry studies of cytochrome c, immobilized on chiral tripeptide monolayer films, reveal the importance of the electron spin and the film's homochirality on electron transfer kinetics. Magnetic film electrodes are used to examine how an asymmetry in the standard heterogeneous electron transfer rate constant arises from changes in the electron spin direction and the enantiomer composition of the tripeptide monolayer; rate constant asymmetries as large as 60% are observed. These findings are rationalized in terms of the chiral induced spin selectivity effect and spin-dependent changes in electronic coupling. Lastly, marked differences in the average rate constant are shown between homochiral ensembles, in which the peptide and protein possess the same enantiomeric form, compared to heterochiral ensembles, where the handedness of the peptide layer is opposite to that of the protein or itself comprises heterochiral building blocks. These data demonstrate a compelling rationale for why nature is homochiral; namely, spin alignment in homochiral systems enables more efficient energy transduction.

Visualization of optical polarization transfer to photoelectron spin vector emitted from a spin-orbit coupled surface state

Similar to light polarization that is selected by a superposition of optical basis, electron spin direction can be controlled through a superposition of spin basis. We investigate such a spin interference occurring in photoemission of the spin-orbit coupled surface state in Bi2Se3 by using spin- and angle-resolved photoemission spectroscopy combined with laser light source (laser-SARPES). Our laser-SARPES with three-dimensional spin detection and tunable laser polarization including elliptical and circular polarization enables us to directly visualize how the direction of the fully-polarized photoelectron spin changes according to the optical phase and orientation of the incident laser polarization. By this advantage of our laser-SARPES, we demonstrate that such optical information can be projected to the three-dimensional spin vector of the photoelectrons. Our results, therefore, present a novel spin-polarized electron source permitting us to optically control the pure spin state pointing to the arbitrary direction.

Spin relevant invariants and the general solution of the Dirac equation for the Coulomb fields

The Dirac equation with the Coulomb potential is studied. A new spin relevant invariant is introduced, which does not commute with the Dirac and Johnson–Lippmann integrals of motion. The solutions of the Dirac equation compatible with each of the above three invariants are found and shown to be different. The explicit expressions for the Dirac bispinors are found for each of the three spin related invariants. The generalized invariant is constructed and corresponding to it general solution of the Dirac equation with the Coulomb potential is obtained. The general solution contains free parameters, whose particular values reduce it to any of the three particular solution. It is shown that the distributions of the electron probability density and expectation values of the electron spin direction in the hydrogen-like energy spectrum depend essentially on the spin relevant invariant. This demonstrates physical difference of the states corresponding to different invariants, which can be experimentally manifested.

Spin Seebeck Effect in a Hybridized Quantum-Dot/Majorana-Nanowire With Spin Heat Accumulation

Properties of spin Seebeck effect (SSE) in a quantum dot (QD) connected to a topological superconductor or semiconductor nanowire with strong spin-orbit interaction are theoretically studied by the noneqilibrium Green’s function method combined with Dyson equation technique. At low temperatures, Majorana zero modes (MZMs) are prepared at the ends of topological superconductor or semiconductor nanowire, and are hybridized to the QD with spin-dependent strength. We consider that the QD is coupled to two leads in the presence of spin heat accumulation (SHA), i.e., spin-dependent temperature in the leads. We find that the thermopower is spin-polarized when the hybridization strength between the QD and one mode of the MZMs depends on electron spin direction, and its spin-polarization can be effectively adjusted by changing the magnitude of SHA. By proper variation of the spin-polarization of the QD-MZM hybridization strength, magnitude of the SHA, dot level, or the direct coupling between the MZMs, 100% spin-polarized or pure thermopower can be generated. Our results may find real usage in high efficiency spintronic devices or detection of the MZMs, which are under current extensive study. The present model is within the reach of current nano-technologies and may by used in high efficiency spin caloritronics devices.

KINETIC BEHAVIOR OF THE INTERACTION BETWEEN TRICALCIUM SILICATE AND LIQUID PHASE

This paper presents a 2D-simulation of the main stages of the tricalcium silicate hardening which reflects a possible mechanism of radical reactions with regard to the spin state of the interacting particles. The principles of the universal static model are used for 2D-simulation. It is shown that the particle charge determines the ionic mechanism. In this case, the electron spin direction does not affect the reaction process. It is demonstrated that the spin direction is important for the interacting particles.

Surface-step defect in three-dimensional topological insulators: Electric manipulation of spin and quantum spin Hall effect

We study the influence of step defect on surface states in three-dimensional topological insulators subject to a perpendicular magnetic field. By calculating the energy spectrum of the surface states, we find that Landau levels (LLs) can form on flat regions of the surface and are distant from the step defect, and several subbands emerge at side surface of the step defect. The subband which connects to the two zeroth LLs is spin-polarized and chiral. In particular, when the electron transports along the side surface, the electron spin direction can be manipulated arbitrarily by gate voltage. And no reflection occurs even if the electron spin direction is changed. This provides a fascinating avenue to control the electron spin easily and coherently. In addition, regarding the subbands with high LL index, there exist spin-momentum locking helical states and the quantum spin Hall effect can appear.

Light and Entanglement Velocities for the Electron and the Proton in Minkowskian Space Require Surface Areas that Approximate the Human Cerebrum: Implications for Excess Correlations

The distinctions between locality and non-locality as well as causality and excess correlation may be related to coupling between increments of space-time or to the total space-time within the universe as a unit. The most likely candidates for the latter are the proton and the electron when related by Minkowski’s space-time. When two velocities: light in a vacuum for locality and the “entanglement” velocity based upon parameters that define the universe for non-locality, are considered the two times required to produce identities for the -v2t2 components are frequencies whose energies approximate the neutral hydrogen line (primarily associated with shifts in electron spin direction) and the mass equivalence of a proton. The values for the additional three spatial dimensions required to produce a solution whose square root is not imaginary and greater than zero are within the domains of the surface areas of the human cerebrum. Detailed calculations converge to show that the proportions of energy that represent the electron’s Compton energy and the proton’s mass equivalent may be central to the condition of excess correlation within the cerebral volume. Proton channels within the neuronal cell plasma membranes whose pH-dependent specific currents produce the required magnetic field strengths could be the physical substrates by which excess correlations between brain activities of human subjects separated by non-local distances might occur. If protons are considered as the basic Eddington (number) units of the universe then Mach’s principle that any component of the universe is determined by all of its components may be testable empirically.

The effect of quantum physics and superconducting logic on future computers

Abstract. While human progress in the world of electronics, computers and computing is undeniable, new researches show that we can achieve greater speed and lower power consumption based on the principles of quantum physics. Changing from the digital world of today, which is based on CMOS transistors and the electric current, to quantum with no electric current and based on magnetic flux, is now in the middle of its way. Clearly any research in this area or even a comprehensive scientific attention is laudable from the experts’ viewpoint. This paper tries to show quantum computers more tangible by describing and analyzing some basic principles and explaining the entrance to this technology. In this article it is explained how the spintronics, superconductivity, and Josephson junction open the ways to the next generation of faster, more compact, and more energy-efficient computers in future; computers that bring about several hundred times the speed and negligible power consumption, along with the revolution of basic principles of electronics. We'll see how the spin transistors transfer data in lower speed and volume, using the electron spin direction to be high or low, or how the superconductivity, which is the key to the future supercomputers, solve the problem of supercomputers power consumption using technologies such as RSFQ.

Spin transport properties of a Dresselhaus-polygonal quantum ring**Project supported by the National Natural Science Foundation of China (Grant No. 61176089), the Natural Science Foundation of Hebei Province, China (Grant No. A2011205092), and the Foundation of Shijiazhuang University, China (Grant No. XJPT002).

We propose a theoretical method to investigate the effect of the Dresselhaus spin–orbit coupling (DSOC) on the spin transport properties of a regular polygonal quantum ring with an arbitrary number of segments. We find that the DSOC can break the time reversal symmetry of the spin conductance in a polygonal ring and that this property can be used to reverse the spin direction of electrons in the polygon with the result that a pure spin up or pure spin down conductance can be obtained by exchanging the source and the drain. When the DSOC is considered in a polygonal ring with Rashba spin–orbit coupling (RSOC) with symmetric attachment of the leads, the total conductance is independent of the number of segments when both of the two types of spin–orbit coupling (SOC) have the same value. However, the interaction of the two types of SOC results in an anisotropic and shape-dependent conductance in a polygonal ring with asymmetric attachment of the leads. The method we proposed to solve for the spin conductance of a polygon can be generalized to the circular model.

Design and Analysis of Radiation Hardened Sensing Circuits for Spin Transfer Torque Magnetic Memory and Logic

CMOS downscaling makes advanced memory and computing systems more vulnerable to radiation. Emerging non-volatile memories such as Magnetic RAM (MRAM) are under development to replace SRAM and FLASH memories. Spin Transfer Torque Magnetic Memory (STT-MRAM) is considered as one of the most promising memories for high reliability appli- cations. This is due to its intrinsic hardness to radiation, as storage is based on the spin direction of electrons instead of the charge. Its peripheral CMOS circuits are sensitive to radiation; however we can recharge frequently the non-volatile storage to get correct data. Different from conventional MRAM based on magnetic field switching, STT-MRAM is unable to be used directly for hard radi- ation applications as the current pulses induced by radiation may change the storage due to the stochastic behaviors of spin transfer torque mechanism. In this paper, we analyze firstly this issue and propose a rad-hard design for STT-MRAM sensing circuit with low area overhead and negligible performance degradation. Both transient and Monte-Carlo simulation have been performed to demonstrate its performance and behaviors.

Effects of Tunable Bloch-Inspired Spin-Orbit Interaction in the Electronic State of Sr2RuO4

The conflicting experimental and theoretical results on the properties of Sr2RuO4 are evidences of its complexities. The Bloch catalytic factor was introduced to investigate the varying interactions between the direction of electron spin and the orbital motion for different ‘d’ elements. The Bloch-inspired spin-orbit interaction (SOI) was designed and tested under the tunable longitudinal and transverse magnetizations. Some of the results correspond to recent experiments. The prevailing SOI in each case is dependent on the splitting of the 4d states.

Transmission and application of electron spin wave function in alternating ferromagnetic and nonmagnetic layers

We establish a general model of a finite periodic system by n pairs of alternating ferromagnetic and nonmagnetic (FNF) layers. Using Bloch spin wave quantum theory, the basic properties of alternating FNF layers and the dependence of property of electron wave scattering in alternating layers on the number of layers are investigated. It is found that an electron wavefunction in the system can be expressed as the superposition of eigenvectors of a transfer matrix or Bloch-like functions in an infinite periodic system. Form this function we can obtain an exact solution for monochromatic wave scattering of a system with an arbitrary number of layers. On this basis, the dependences of reflection and transmission coefficients on energy for the electron wavefunction in a periodic system are determined. The calculation of spectral window shows that its energy position and width are the same as those of almost full reflection region. The system can be used as spin filter due to high-energy dispersion and dependence of exchange energy on electron spin direction.

Spin coherence generation and detection in spherical nanocrystals

A theoretical description of electron spin orientation and detection by short optical pulses is proposed for ensembles of singly charged semiconductor nanocrystals. The complex structure of the valence band in spherical nanocrystals is taken into account. We demonstrate that the direction of electron spin injected by the pump pulse depends on both the pump pulse helicity and the pump pulse power. It is shown that a train of optical pulses can lead to the complete orientation of the resident electron spin. The microscopic theory of the spin Faraday, Kerr and ellipticity effects is developed and the spectral sensitivity of these signals is discussed. We show that under periodic pumping pronounced mode-locking of electron spins takes place and manifests itself as significant spin signals at negative delays between pump and probe pulses.

Anisotropic Spin Splitting in Step Quantum Wells

By the method of finite difference, the anisotropic spin splitting of the AlxGa1–xAs/GaAs/AlyGa1–yAs/AlxGa1–xAs step quantum wells (QWs) are theoretically investigated considering the interplay of the bulk inversion asymmetry and structure inversion asymmetry induced by step quantum well structure and external electric field. We demonstrate that the anisotropy of the total spin splitting can be controlled by the shape of the QWs and the external electric field. The interface related Rashba effect plays an important effect on the anisotropic spin splitting by influencing the magnitude of the spin splitting and the direction of electron spin. The Rashba spin splitting presents in the step quantum wells due to the interface related Rashba effect even without external electric field or magnetic field.

Generalization of Faraday’s Law to Include Nonconservative Spin Forces

The usual Faraday's Law E=-dPhi/dt determines an electromotive force E which accounts only for forces resulting from the charge of electrons. In ferromagnetic materials, in general, there exist nonconservative spin forces which also contribute to E. These might be included in Faraday's Law if the magnetic flux Phi is replaced by [Planck's constant/(-e)]gamma, where gamma is a Berry phase suitably averaged over the electron spin direction. These contributions to E represent the requirements of energy conservation in itinerant ferromagnets with time dependent order parameters.

Electron transmission across ferromagnetic layers

Movement of spin-polarized electrons through a finite periodic system formed by n pairs of alternating ferromagnetic and nonmagnetic layers is considered. General features of electron scattering in super layers and their dependence on a number of layers are described. An electron wave function is found in one-dimension rectangular potential with finite number of periods. It is written as superposition of eigenvectors of a translation matrix or Bloch-like functions for an infinite periodic system. We obtain an exact solution for scattering of monochromatic wave on a system with an arbitrary number of layers. Energy dependence of a reflection and transmission coefficients is presented in an explicit symbol form. Number of spectral windows, their energy positions and widths are found as well as regions of almost full reflection. The system can be used as spin filter due to high-energy dispersion and dependence of exchange energy on electron spin direction.

Extended theory of Kapitza-Dirac scattering

The standard theoretical treatment of the Kapitza-Dirac effect---that is, the scattering of an electron passing through a standing-wave laser field---is extended here through the use of the Pauli equation to account for the interaction of the electron spin with the magnetic field of the standing wave. Prescriptions for determining unitarity-preserving approximations for the transition probabilities for scattering both with and without rotation of the electron spin direction are provided. This formalism is used to develop a perturbation theory for the spin-flip probability which, in the strong-field limit of interest here, reduces to a fairly simple relation between $S$-matrix elements for scattering with and without change in spin orientation, each expressed in terms of a Bessel function. A similar perturbative procedure is applied to estimate corrections to the standard theory for scattering in the absence of spin-flip processes, in which interactions that change the net number of photons in the field are ignored.

Reversal of local spins in transport of electrons through a one-dimensional chain

We investigate the spin reversal of two coupled magnetic impurities in the transport processes of electrons in a one-dimensional chain. The impurities are side coupled to the chain and the electrons are injected and tunneling through it. The transmission coefficient of electrons and the polarization of impurities are calculated by the use of the equivalent single-particle network method for the correlated system. It is found that both the transmission coefficient and the polarization of impurities depend on the initial state of impurities and the impurity spins can be converted into the direction of electron spin if the injected electrons are polarized and the number of electrons is large enough. The evolution of the spin-reversal processes is studied in details.