Spin hall effect in the presence of spin diffusion

Hirsch [Phys. Rev. Lett. 83, 1834 (1999)] recently proposed a spin Hall effect based on the anomalous scattering mechanism in the absence of spin-flip scattering. Since the anomalous scattering causes both anomalous currents and a finite spin-diffusion length, we derive the spin Hall effect in the presence of spin diffusion from a semiclassical Boltzmann equation. When the formulation is applied to certain metals and semiconductors, the magnitude of the spin Hall voltage due to the spin accumulation is found to be much larger than that of magnetic multilayers. An experiment is proposed to measure this spin Hall effect.     

Switching the direction of spin accumulation in the spin Hall effect of light by adjusting the optical axis of an uniaxial crystal

We theoretically and experimentally investigate a switchable spin Hall effect (SHE) of light in reflection near the Brewster angle at an air-uniaxial crystal interface. We find a large transverse spin splitting near the Brewster angle, whose sign can be altered by rotating the optical axis. As an analogy of the SHE in an electronic system, a switchable spin accumulation in the SHE of light is detected. We are able to switch the direction of the spin accumulation by adjusting the optical axis angle of the uniaxial crystal. These findings may give opportunities for photon spin manipulating and developing a new generation of nano-photonic devices.     

Intrinsic spin Hall effect in platinum: first-principles calculations

Spin Hall effect (SHE) is studied with first-principles relativistic band calculations for platinum, which is one of the most important materials for metallic SHE and spintronics. We find that intrinsic spin Hall conductivity (SHC) is as large as approximately 2000(variant Planck's over 2 pi/e)(Omega cm)(-1) at low temperature and decreases down to approximately 200(variant Planck's over 2 pi/e)(Omega cm)(-1) at room temperature. It is due to the resonant contribution from the spin-orbit splitting of the doubly degenerated d bands at high-symmetry L and X points near the Fermi level. By modeling these near degeneracies by an effective Hamiltonian, we show that SHC has a peak near the Fermi energy and that the vertex correction due to impurity scattering vanishes. We therefore argue that the large SHE observed experimentally in platinum is of intrinsic nature.     

Spin-torque ferromagnetic resonance induced by the spin Hall effect

We demonstrate that the spin Hall effect in a thin film with strong spin-orbit scattering can excite magnetic precession in an adjacent ferromagnetic film. The flow of alternating current through a Pt/NiFe bilayer generates an oscillating transverse spin current in the Pt, and the resultant transfer of spin angular momentum to the NiFe induces ferromagnetic resonance dynamics. The Oersted field from the current also generates a ferromagnetic resonance signal but with a different symmetry. The ratio of these two signals allows a quantitative determination of the spin current and the spin Hall angle.     

The family of topological Hall effects for electrons in skyrmion crystals

Hall effects of electrons can be produced by an external magnetic field, spin–orbit coupling or a topologically non-trivial spin texture. The topological Hall effect (THE) – caused by the latter – is commonly observed in magnetic skyrmion crystals. Here, we show analogies of the THE to the conventional Hall effect (HE), the anomalous Hall effect (AHE), and the spin Hall effect (SHE). In the limit of strong coupling between conduction electron spins and the local magnetic texture the THE can be described by means of a fictitious, “emergent” magnetic field. In this sense the THE can be mapped onto the HE caused by an external magnetic field. Due to complete alignment of electron spin and magnetic texture, the transverse charge conductivity is linked to a transverse spin conductivity. They are disconnected for weak coupling of electron spin and magnetic texture; the THE is then related to the AHE. The topological equivalent to the SHE can be found in antiferromagnetic skyrmion crystals. We substantiate our claims by calculations of the edge states for a finite sample. These states reveal in which situation the topological analogue to a quantized HE, quantized AHE, and quantized SHE can be found.     

Orbitronics: the intrinsic orbital current in p-doped silicon

The spin Hall effect depends crucially on the intrinsic spin-orbit coupling of the energy band. Because of the smaller spin-orbit coupling in silicon, the spin Hall effect is expected to be much reduced. We show that an electric field in p-doped silicon can induce a dissipationless orbital current in a fashion reminiscent of the spin Hall effect. The vertex correction from impurity scattering vanishes and the effect is robust against disorder. The orbital Hall effect leads to accumulation of local orbital momentum at the edge of the sample, and can be detected by the Kerr effect.     

掺铌SrTiO_3中的逆自旋霍尔效应

采用磁控溅射法在未掺杂和掺杂的SrTiO_3基片上沉积了NiFe薄膜,通过翻转测试法分离出掺杂样品中的自旋整流电压和逆自旋霍尔电压.研究结果表明:在未掺杂的SrTiO_3基片中,翻转前后测试的电压曲线基本一致,为NiFe薄膜自旋整流效应产生的电压.对于掺Nb浓度x为0.028, 0.05, 0.1, 0.15, 0.2的SrTiO_3基片,分离出的逆自旋霍尔电压随掺杂浓度增加而减小,在掺杂浓度为0.15和0.2的样品中没有探测到明显的逆自旋霍尔电压.本文的结果表明,在SrTiO_3中掺入强自旋轨道耦合的杂质,通过掺杂浓度可以实现对SrTiO_3中逆自旋霍尔效应的调控,这类可调控的自旋相关研究为自旋电子器件的研究和开发提供了更多的可能性,具有很大的潜在应用价值.     

多层介质中的光自旋霍尔效应研究

本文研究了光束通过多层介质分界面的光自旋霍尔效应. 以三层介质为例,建立了光束通过棱镜-空气-棱镜结构的传输模型,揭示了横移与空气介质的厚度、折射率梯度以及入射角等因素的定性关系. 发现对某一特定的圆偏振光束,改变两棱镜之间的折射率梯度可以调控横移,反射场与传输场的横移方向取决于折射率梯度. 相对于两层介质来说,高斯光束通过三层介质能明显地增强光自旋霍尔效应. 研究多层介质中光自旋霍尔效应横移的影响因素可为调控和增强光自旋霍尔效应提供理论依据. 关键词： 光自旋霍尔效应 横移 折射率梯度     

Spin-to-orbital angular momentum conversion in spin Hall effect of light

From the viewpoint of classical electrodynamics, we identify the role of spin-to-orbital angular momentum conversion in spin Hall effect (SHE) of light. We introduce a distinct separation between spin and orbital angular momenta to clarify the spin–orbital interaction in conventional beam refraction. We demonstrate that the refractive index gradient can enhance or suppress the spin-to-orbital angular momentum conversion, and thus can control the SHE of light. We suggest that the metamaterial whose refractive index can be tailored arbitrarily may become a good candidate for amplifying or eliminating the SHE of light, and by properly facilitating the spin-to-orbital angular momentum conversion the SHE may be enhanced dramatically. The transverse spatial shifts governed by the spin-to-orbital angular momentum conversion, provide us a clear physical picture to clarify the role of refractive index gradient in the SHE of light. These findings provide a pathway for modulating the SHE of light and can be extrapolated to other physical systems.     

Spin current transmission in Co1-xTbx films

We investigate the spin to charge conversion phenomena in Y₃Fe₅O₁₂/Pt/Co_1-xTb_x/Pt multilayers by both the spin pumping and spin Seebeck effects.We find that the spin transport efficiency is irrelevant to magnetization states of the perpendicular magnetized Co;Tb;films,which can be attributed to the symmetry requirement of the inverse transverse spin Hall effect.Furthermore,the spin transmission efficiency is significantly affected by the film concentration,revealing the dominant role of extrinsic impurity scattering caused by Tb impurity.The present results provide further guidance for enhancing the spin transport efficiency and developing spintronic devices.     

Photonic spin Hall effect in PT symmetric metamaterials

We proposed and demonstrated that PT symmetric metamaterials could be used to achieve enhanced spin Hall effect (SHE) of light. We find that when laser mode is excited in PT symmetric system, the enhanced SHE could be obtained in both transmitted and reflected beams. In addition, as exceptional points (EPs) of PT symmetric system can happen for both p- and s-polarizations, the enhanced SHE of reflected light can function for both horizontally and vertically polarized incident beams. Particularly, these EPs can lead to unidirectional reflectionlessness, asymmetric SHE with maximum contrast ratio of 48 is obtained by launching light beams near EPs. Our work opens up a new path to obtain enhanced transverse displacement for both reflected and transmitted light and enables more opportunities in manipulating photonic SHE.     

光子自旋霍尔效应及其在物性参数测量中的应用

光子自旋霍尔效应是指光束在非均匀介质中传输时,自旋角动量相反的光子在垂直于入射 面的方向发生的横向自旋相关分裂。光子自旋霍尔效应可以和电子自旋霍尔效应作类比：自旋光 子扮演自旋电子的角色,折射率梯度扮演外场的角色。光子自旋霍尔效应源于光的自旋-轨道相互 作用,和两类几何相位有关：一类是动量空间的自旋重定向Rytov-Vlasimirskii-Berry 相位;另 一类是斯托克斯参数空间的Pancharatnam-Berry 相位。光子自旋霍尔效应对物性参数非常敏感, 结合量子弱测量技术,在物性参数测量、光学传感等领域具有重要的应用前景。本文将简单分析 光子自旋霍尔效应的物理根源,回顾近几年不同物理系统中光子自旋霍尔效应的研究进展,介绍 光子自旋霍尔效应在物性参数测量中的应用。最后,展望其在光学模拟运算、显微成像、量子成 像等领域的可能发展方向。     

Extrinsic spin Hall effect induced by iridium impurities in copper

We study the extrinsic spin Hall effect induced by Ir impurities in Cu by injecting a pure spin current into a CuIr wire from a lateral spin valve structure. While no spin Hall effect is observed without Ir impurity, the spin Hall resistivity of CuIr increases linearly with the impurity concentration. The spin Hall angle of CuIr, (2.1±0.6)% throughout the concentration range between 1% and 12%, is practically independent of temperature. These results represent a clear example of predominant skew scattering extrinsic contribution to the spin Hall effect in a nonmagnetic alloy.     

Interplay of Rashba effect and spin Hall effect in perpendicular Pt/Co/MgO magnetic multilayers

The interplay of the Rashba effect and the spin Hall effect originating from current induced spin–orbit coupling was investigated in the as-deposited and annealed Pt/Co/MgO stacks with perpendicular magnetic anisotropy. The above two effects were analyzed based on Hall measurements under external magnetic fields longitudinal and vertical to dc current,respectively. The coercive field as a function of dc current in vertical mode with only the Rashba effect involved decreases due to thermal annealing. Meanwhile, spin orbit torques calculated from Hall resistance with only the spin Hall effect involved in the longitudinal mode decrease in the annealed sample. The experimental results prove that the bottom Pt/Co interface rather than the Co/MgO top one plays a more critical role in both Rashba effect and spin Hall effect.     

Observation of intrinsic inverse spin Hall effect

We report observation of intrinsic inverse spin Hall effect in undoped GaAs multiple quantum wells with a sample temperature of 10 K. A transient ballistic pure spin current is injected by a pair of laser pulses through quantum interference. By time resolving the dynamics of the pure spin current, the momentum relaxation time is deduced, which sets the lower limit of the scattering time between electrons and holes. The transverse charge current generated by the pure spin current via the inverse spin Hall effect is simultaneously resolved. We find that the charge current is generated well before the first electron-hole scattering event. Generation of the transverse current in the scattering-free ballistic transport regime provides unambiguous evidence for the intrinsic inverse spin Hall effect.     

Photonic spin Hall effect and terahertz gas sensor via InSb-supported long-range surface plasmon resonance

We propose a simple one-dimensional grating coupling system that can excite multiple surface plasmon resonances for refractive index(RI)sensing with self-reference characteristics in the near-infrared band.Using theoretical analysis and the finite-difference time-domain method,the plasmonic mechanism of the structure is discussed in detail.The results show that the excited resonances are independent of each other and have different fields of action.The mode involving extensive interaction with the analyte environment achieves a high sensitivity of 1236 nm/RIU,and the figure of merit(FOM)can reach 145 RIU-1.Importantly,the mode that is insensitive to the analyte environment exhibits good self-reference characteristics.Moreover,we discuss the case of exchanging the substrate material with the analyte environment.Promising simulation results show that this RI sensor can be widely deployed in unstable and complicated environments.     

Spin pumping with coherent elastic waves

We show that the resonant coupling of phonons and magnons can be exploited to generate spin currents at room temperature. Surface acoustic wave pulses with a frequency of 1.55 GHz and duration of 300 ns provide coherent elastic waves in a ferromagnetic thin-film-normal-metal (Co/Pt) bilayer. We use the inverse spin Hall voltage in the Pt as a measure for the spin current and record its evolution as a function of time and external magnetic field magnitude and orientation. Our experiments show that a spin current is generated in the exclusive presence of a resonant elastic excitation. This establishes acoustic spin pumping as a resonant analogue to the spin Seebeck effect.     

Electrical measurement of the direct spin hall effect in Fe/InxGa(1-x)As heterostructures

We report on an all-electrical measurement of the spin Hall effect in epitaxial Fe/InxGa(1-x)As heterostructures with n-type (Si) channel doping and highly doped Schottky tunnel barriers. A transverse spin current generated by an ordinary charge current flowing in the InxGa(1-x)As is detected by measuring the spin accumulation at the edges of the channel. The spin accumulation is identified through the observation of a Hanle effect in the voltage measured by pairs of ferromagnetic Hall contacts. We investigate the bias and temperature dependence of the resulting Hanle signal and determine the skew and side-jump contributions to the total spin Hall conductivity.     

Optical spin hall effect

A remarkable analogy is established between the well-known spin Hall effect and the polarization dependence of Rayleigh scattering of light in microcavities. This dependence results from the strong spin effect in elastic scattering of exciton polaritons: if the initial polariton state has a zero spin and is characterized by some linear polarization, the scattered polaritons become strongly spin polarized. The polarization in the scattered state can be positive or negative dependent on the orientation of the linear polarization of the initial state and on the direction of scattering. Very surprisingly, spin polarizations of the polaritons scattered clockwise and anticlockwise have different signs. The optical spin Hall effect is possible due to strong longitudinal-transverse splitting and finite lifetime of exciton polaritons in microcavities.     

Electric manipulation of spin relaxation using the spin Hall effect

Using the spin Hall effect, magnetization relaxation in a Ni_{81}Fe_{19}/Pt film is manipulated electrically. An electric current applied to the Pt layer exerts spin torque on the entire magnetization of the Ni81Fe19 layer via the macroscopic spin transfer induced by the spin Hall effect and modulates the magnetization relaxation in the Ni81Fe19 layer. This method allows us to tune the magnetization dynamics regardless of the film size without applying electric currents directly to the magnetic layer.