Electric modulation of the Fermi arc spin transport via three-terminal configuration in topological semimetal nanowires

Spin–momentum locking is a key feature of the topological surface state, which plays an important role in spintronics.The electrical detection of current-induced spin polarization protected by the spin–momentum locking in nonmagnetic systems provides a new platform for developing spintronics, while previous studies were mostly based on magnetic materials.In this study, the spin transport measurement of Dirac semimetal Cd_(3)As_(2) was studied by three-terminal geometry, and a hysteresis loop signal with high resistance and low resistance state was observed. The hysteresis was reversed by reversing the current direction, which illustrates the spin–momentum locking feature of Cd_(3)As_(2). Furthermore, we realized the on–off states of the spin signals through electric modulation of the Fermi arc via the three-terminal configuration, which enables the great potential of Cd_(3)As_(2) in spin field-effect transistors.

Optical spin-to-orbital angular momentum conversion in structured optical fields

We investigate the dynamic quantities:momentum,spin and orbital angular momenta(SAM and OAM),and their conversion relationship in the structured optical fields at subwavelength scales,where the spin–orbit interaction(SOI)plays a key role and determines the behaviors of light.Specifically,we examine a nanostructure of a Ag nanoparticle(Ag NP)attached on a cylindrical Ag nanowire(Ag NW)under illumination of elliptically polarized light.These dynamic quantities obey the Noether theorem,i.e.,for the Ag nanoparticle with spherical symmetry,the total angular momentum consisting of SAM and OAM conserves;for the Ag NW with translational symmetry,the orbital momentum conserves.Meanwhile,the spin-to-orbital angular momentum conversion is mediated by SOI arising from the spatial variation of the optical potential.In this nanostructure,the conservation of momentum imposes a strict restriction on the propagation direction of the surface plasmon polaritons along the Ag NW.Meanwhile,the orbital momentum is determined by the polarized properties of the excitation light and the topography of the Ag NP.Our work offers insights to comprehend the light behaviors in the structured optical fields in terms of the dynamic quantities and benefits to the design of optical nano-devices based on interactions between spin and orbital degrees of freedom.

Asymmetrical spiral spectra and orbital angular momentum density of non-uniformly polarized vortex beams in uniaxial crystals

To explore the effect of non-uniform polarization on orbital angular momentum(OAM) in anisotropic medium, in this work investigated are the evolution of the spiral spectra and OAM densities of non-uniformly polarized vortex(NUPV)beams in uniaxial crystals propagating orthogonal to the optical axis, and also the case of uniformly polarized vortex(UPV)beams with left-handed elliptical polarization. In the input plane, the NUPV beams present their spiral spectra of m-mode concentrated at m = l ± 1 modes rather than m = l mode, and reveal the relation among topological charge l, mode of spiral spectra m and the power weight value Rmexpressed by l=∑^(∞)_(m)=-∞Rm. is still satisfied for UPV beams in uniaxially anisotropic crystals, whereas for NUPV beams their relations are no longer valid owing to non-uniform polarization. Furthermore, the analysis indicates that the asymmetrical distribution of power weight of spiral spectra and the non-zero value in the sum of longitudinal OAM densities originate from the initial non-uniform polarization and anisotropy in uniaxial crystals rather than topological charges. In addition, the relation between spiral spectrum and longitudinal OAM density is numerically discussed. This work may provide an avenue for OAM-based communications,optical metrology, and imaging by varying the initial non-uniform polarization.

Electrical spin polarization through spin-momentum locking in topological-insulator nanostructures

Recently, spin-momentum-locked topological surface states（SSs） have attracted significant attention in spintronics.Owing to spin-momentum locking, the direction of the spin is locked at right angles with respect to the carrier momentum.In this paper, we briefly review the exotic transport properties induced by topological SSs in topological-insulator（TI）nanostructures, which have larger surface-to-volume ratios than those of bulk TI materials. We discuss the electrical spin generation in TIs and its effect on the transport properties. A current flow can generate a pure in-plane spin polarization on the surface, leading to a current-direction-dependent magnetoresistance in spin valve devices based on TI nanostructures.A relative momentum shift of two coupled topological SSs also generates net spin polarization and induces an in-plane anisotropic negative magnetoresistance. Therefore, the spin-momentum locking can enable the broad tuning of the spin transport properties of topological devices for spintronic applications.

Change in Mass of Spinning Black Holes w.r.t. the Angular Momentum

Mahto et al. have shown δS≥0 and M2=a*J by using the first law of the black hole mechanics in the vacuum and Einstein mass-energy equivalence relation specially for spinning black holes. In the present paper, this work is extended to propose a model for the change in mass of the spinning black holes due to corresponding change in the angular momentum for maximum & half spin parameter of black holes (a* = 1 & 1/2) and calculated their values for different test black holes in XRBs and AGN. We have also shown that the change in mass of the spinning black holes due to corresponding change in the angular momentum for maximum spinning rate of black holes (a* = 1) is double to that of the spinning black holes having spinning parameter (a* = 1/2).

Magnetic Charge Theory Part 4: Fermion Angular Momentum

The magnetic charge concept is further developed to define the vibrational motion of a charged particle moving in the ether/dark matter. The angular momentum of the resulting motion is derived to be ħ/2 at all velocities. The vibrational motion also provides additional justification for the Coulomb and gravitational forces not having a singularity. Additional insights into antimatter composition and annihilation are also developed.

The Definition of Universal Momentum Operator of Quantum Mechanics and the Essence of Micro-Particle’s Spin——To Reveal the Real Reason That the Bell Inequality Is Not Supported by Experiments

The definition of momentum operator in quantum mechanics has some foundational problems and needs to be improved. For example, the results are different in general by using momentum operator and kinetic operator to calculate microparticle’s kinetic energy. In the curved coordinate systems, momentum operators can not be defined properly. When momentum operator is acted on non-eigen wave functions in coordinate space, the resulting non-eigen values are complex numbers in general. In this case, momentum operator is not the Hermitian operator again. The average values of momentum operator are complex numbers unless they are zero. The same problems exist for angle momentum operator. Universal momentum operator is proposed in this paper. Based on it, all problems above can be solved well. The logical foundation of quantum mechanics becomes more complete and the EPY momentum paradox can be eliminated thoroughly. By considering the fact that there exist a difference between the theoretical value and the real value of momentum, the concepts of auxiliary momentum and auxiliary angle momentum are introduced. The relation between auxiliary angle momentum and spin is deduced and the essence of micro-particle’s spin is revealed. In this way, the fact that spin gyro-magnetic ratio is two times of orbit gyro-magnetic ratio, as well as why the electrons of ground state without obit angle momentum do not fall into atomic nuclear can be explained well. The real reason that the Bell inequality is not supported by experiments is revealed, which has nothing to do with whether or not hidden variables exist, as well as whether or not locality is violated in microcosmic processes.

基于梯度结构波导实现的定向声学自旋角动量密度操控

近年来,人们在结构声场和声学结构表面波中发现了声波横向自旋的现象,其不仅丰富了人们对声波基本性质的理解,也为操控声波提供了新的途径.在本文中,我们设计了平整型、上凸型、下凹型的梯度声学波导,实现对声学表面波的横向自旋分布进行操控.通过理论分析和数值仿真,研究了自旋声源在3种梯度结构中激发的压力场分布以及自旋角动量密度分布,验证了近场声自旋-动量的方向锁定,展示了梯度波导中声表面波的自旋强度分布操控.研究结果可能促进对声学近场物理的对称性理解,以及提供一种操控声学自旋角动量密度的方法,为利用声波操控粒子开辟新的路径.

自旋轨道角动量耦合的超流费米气体

近年来,自旋轨道耦合的原子气体研究取得了许多重要的进展,其中一种新近实现的新类型自旋轨道耦合-自旋轨道角动量耦合由于其独特性质吸引了人们的兴趣。本文以费米气体为例,介绍自旋轨道角动量耦合的实现和特点,以及对单粒子谱特别是对费米超流的重要影响。结合平均场解析方法和数值模拟,分析了自旋轨道角动量耦合诱导的有限角动量配对和由此导致的不同类型的超流涡旋基态,并进一步讨论了相关的进展和未来可能的发展方向。

Change in Entropy of Spinning Black Holes Due to Corresponding Change in Mass in XRBs

The present paper gives a theoretical model for the change in entropy of spinning black holes due to change in mass to use the first law of black hole mechanics for unit spinning parameter and angular momentum in XRBs. This shows that the entropy change with respect to the mass of uncharged spinning black holes is essentially the function of mass and their surface gravity are lesser than to that of the non-spinning black holes.

A Formulation of Spin Dynamics Using Schrodinger Equation

In quantum mechanics, there is a profound distinction between orbital angular momentum and spin angular momentum in which the former can be associated with the motion of a physical object in space but the latter cannot. The difference leads to a radical deviation in the formulation of their corresponding dynamics in which an orbital angular momentum can be described by using a coordinate system but a spin angular momentum cannot. In this work, we show that it is possible to treat spin angular momentum in the same manner as orbital angular momentum by formulating spin dynamics using Schrödinger equation in an intrinsic coordinate system. As an illustration, we apply the formulation to the dynamics of a hydrogen atom and show that the intrinsic spin angular momentum of the electron can take half-integral values and, in particular, the intrinsic mass of the electron can take negative values. We also consider a further extension by generalising the formulation so that it can be used to describe other intrinsic dynamics that may associate with a quantum particle, for example, when a hydrogen atom radiates a photon, the photon associated with the electron may also possess an intrinsic dynamics that can be described by an intrinsic wave equation that has a similar form to that for the electron.

A New Theory for the Essence and Origin of Electron Spin

Spin is an intrinsic form of angular momentum carried by elementary particles, composite particles, and atomic nuclei. It is wildly believed that spin is a purely quantum mechanical concept and has no classical analogue. In fact, elementary particles are conceived as point objects which have no axis to “spin” around. Therefore, there is no explaining how spin arises at the fundamental level, why particles have the values they do, and what underpins the Pauli Exclusion principle and Bose-Einstein behavior. However, spin is like a vector quantity;it has a definite magnitude, and it has a “direction”, in order to spin should be composite. In this paper we propose a physical explanation for spin of the electron at the sub-particle level, relying on the vortex model of the electron. The electron is described as a superfluid frictionless vortex which has a mass, angular momentum and spin to provide a complete explanation of all properties of the electron: it composite, spinning around its own axis, produces a tiny magnetic fields independent of those from its orbital motions. The classical hydrodynamic laws are used to describe the quantum properties of the electron, such as spin, angular momentum, magnetic momentum and a magnetic dipole. The circulation in the vortex is constant, and the angular momentum of the vortex is conserved and has the same value of Planck constant. The direction of the angular momentum of a spinning electron vortex is along the axis of rotation and determined by the direction of spin. The spin quantum number 1/2 has a fixed value which represents the gap between the circulation rate of the core of the vortex and the boundaries of the vortex. The changeable values +1/2 “spin-up” or -1/2 “spin-down” indicate the direction of the magnetic dipole of the vortex. The relation between spin and Planck constant is discussed and the origin h/4pi angular momentum units are revealed.

自旋张量-动量耦合玻色-爱因斯坦凝聚的动力学性质

利用高斯变分近似及基于Gross-Pitaevskii方程的数值求解,研究了一维自旋张量-动量耦合玻色-爱因斯坦凝聚中平面波态的动力学性质,发现基态为双轴向列态,其动量随Raman耦合强度的增加而单调递减.在微扰作用下,基态具有动力学稳定性,且展现出3种不同的谐振模激发,激发频率与Raman耦合强度、谐振子势阱的纵横比及相互作用强度有关.通过数值求解变分参数满足的运动方程和Gross-Pitaevskii方程,发现体系随时间演化将展现出周期性振荡行为.

圆偏振涡旋光致非轴向自旋和轨道运动研究

为了实现粒子的非轴向旋转操控,对圆偏振涡旋光的光致旋转特性进行了研究。理论上,利用T矩阵理论,计算光场作用于微粒的光力和力矩,分析圆偏振涡旋光场中自旋角动量和轨道角动量的取向对非轴向旋转效应的影响。研究结果表明:当轨道角动量和自旋角动量的方向相同时,粒子除受轨道矩和轴向自旋矩作用外,还受一个可观的横向自旋矩作用,可以诱导粒子同时做轨道和非轴向自旋运动;当轨道角动量和自旋角动量方向相反,则粒子受到的横向自旋矩难以驱动其做非轴向自旋运动。实验上,利用全息光镊系统捕获微米尺度的粒子,观察到粒子做轨道运动时的非轴向自旋现象,对理论研究结果进行了初步验证。

石墨烯表面涡旋光束的局域动力学特性分析

结合角谱展开方法和矢量势方法,推导了拉盖尔高斯涡旋光束在石墨烯表面反射后的电磁场分量显式表达式。分析了光束的入射角和拓扑荷数,以及石墨烯-衬底系统的费米能量和磁场对涡旋光束在石墨烯表面反射后局域动力学特性的影响。数值结果表明,石墨烯表面反射涡旋光束的能量、动量、自旋/轨道角动量密度分布随着光束入射角和拓扑荷数的变化发生显著变化。同时,改变石墨烯-衬底系统的费米能量和磁场可以有效调节反射涡旋光束的局域动力学特性。为基于涡旋光束局域动力学特性对石墨烯的表征以及基于石墨烯对涡旋光束的调控奠定了理论基础。

自旋张量-动量耦合作用下自旋1玻色-爱因斯坦凝聚体的调制不稳定性

研究了自旋张量-动量耦合作用下自旋1玻色-爱因斯坦凝聚体(BEC)中连续波态的调制不稳定性.借助于扰动频率和波数之间的色散关系,研究发现系统的调制不稳定性可以用六个不等价的分支来充分描述.进一步分析表明,在给定拉曼耦合强度和原子-原子相互作用强度下,动量空间中调制不稳定增长率分布关于k=0是对称的,并可用若干不同的不稳定带来表征.本文也计算了在相同参数条件下自旋-轨道耦合自旋1 BEC中调制不稳定的增长率,并与前者的结果进行了比较.除了不同的谱带数目和谱带强度外,具有自旋-轨道耦合BEC的调制不稳定性实际上只与三个不等价的分支有关,这源于它与具有自旋张量-动量耦合BEC系统的单粒子哈密顿量的不同对称性.这些结果不仅有助于人们理解系统基态的非线性动力学性质,而且有助于对系统中可能存在的非线性激发进行系统分析.

均匀偏振cosh-Pearcey-Gauss光束的远场坡印廷矢量,自旋与轨道角动量

本文提出了均匀偏振cosh-Pearcey-Gauss光束,其主要由双曲余弦函数(n,Ω)和偏振相关角度(α,δ)所调制。基于矢量角谱法和稳相法,研究了该光束的远场坡印廷矢量、自旋角动量和轨道角动量。研究结果表明:较大的双曲余弦函数值能将远场坡印廷矢量、自旋角动量和轨道角动量分割成多瓣抛物线结构。虽然左旋和右旋椭圆偏振不能影响整个光束结构,但却可通过调节TE和TM项的左半边和右半边的分布权重,进而分辨出光束的远场坡印廷矢量和角动量分布。本文结果对信息存储与偏振成像技术领域有着潜在的应用价值。

相对论涡旋高次谐波的产生与调控理论研究

目前,具有螺旋相位波前和环状光强分布的涡旋光束已在光学领域获得了广泛应用,其产生与调控自然成了研究的热点。利用三维粒子模拟程序对双色拉盖尔高斯激光驱动固体等离子激发同时携带自旋角动量与轨道角动量的高次谐波的物理过程进行了研究,根据高次谐波产生过程中的光子能量与角动量守恒定律对其内在物理机制进行了理论分析,并讨论了对谐波阶次、偏振态(自旋角动量)以及拓扑荷数(轨道角动量)进行调控的方法。研究结果为开发高亮度、超短超快、短波长、自旋与轨道角动量可调控的涡旋光束辐射源提供了理论依据,在光学微操控、超分辨成像、光通信以及离子加速等领域具有较大的实际应用前景。

隐失波横自旋的若干物理性质研究

该文对隐失波横自旋展开了一些新的研究,得到以下结果:1)获得横自旋的量子化形式;2)从统一的观点来看,横自旋归因于隐失波等效静止质量的存在;3)横自旋同样可以采用光子场的自旋矩阵来描述;4)对于真空中的自由光场而言,只有其传播方向上的自旋投影才是可观测量,而隐失场由于存在等效的静止质量,它在其他方向上的自旋投影也可以是可观测量,因此可以类比于自旋电子学,发展一门新的学科,即自旋光子学。

双折射晶体微粒光致旋转受其半径影响分析

利用双折射晶体微粒在具有自旋角动量的光束作用下可产生围绕自身光轴旋转的特性,在光镊实验平台上实现了双折射晶体微粒的光致旋转。为了提高晶体微粒的旋转频率,从理论和实验上对双折射晶体微粒的旋转频率受其半径的影响进行了分析。用MATLAB模拟出CaCO3晶体微粒和SiO2晶体微粒的旋转频率与其半径的三次方成反比的关系曲线,并测得相应的实验关系曲线,其结果与理论分析相吻合。在相同的激光功率下,CaCO3晶体微粒的最高旋转频率可达15.1 Hz,SiO2晶体微粒的最高旋转频率可达11.4 Hz。该结论可用于光致旋转在实际应用中晶体微粒大小的选择和其旋转频率的优化控制。