Giant Spin Hall Effect Research Articles

Giant and nonreciprocal photonic spin hall effect in asymmetric multilayered structure with bulk dirac semimetal

Abstract The nonreciprocal photonic spin Hall effect features the different reflected or transmitted spin shifts along two opposite incident wave propagating directions. However, previous investigations have always focused on the features of the photonic spin Hall effect along one incident wave propagating direction. How to achieve the nonreciprocal photonic spin Hall effect remains obscure. Here, we theoretically study the nonreciprocal photonic spin Hall effect in the asymmetric multilayered structure containing the Bulk Dirac Semimetal and other dielectric materials. It is found that under the horizontal polarization the maximum reflected spin shift value along one direction is up to around times of the incident wavelength at , but it is only times of the incident wavelength at along the other direction, which reflects the nonreciprocity of photonic spin Hall effect and thus can act as the photonic spin Hall diode. Such a sizeable directional difference between the reflected spin shifts along these two opposite directions originates from the fact that this structure loses its mirror symmetry and becomes an asymmetrical one, and the obvious difference in the values of the reflected spin shifts along the two directions can be attributed to the large difference in the values of . At the same time, we find that the Fermi energy of the Bulk Dirac Semimetal can effectively tune the spin shift along the backward direction, as well as the difference between the spin shifts for two different propagating directions, which causes the controllable nonreciprocal photonic spin Hall effect. Our results establish the alternative configuration for realizing the nonreciprocal photonic spin Hall effect, which facilitates the potential applications in the spin photonic devices.

Emergent Quantum Phenomena of a Noncentrosymmetric Charge Density Wave in 1T-Transition Metal Dichalcogenides.

1T-transition metal dichalcogenides (TMDs) have been an exciting platform for exploring the intertwinement of charge density waves and strong correlation phenomena. While the David star structure has been conventionally considered as the underlying charge order in the literature, recent scanning tunneling probe experiments on several monolayer 1T-TMD materials have motivated a new, alternative structure, namely, the anion-centered David star structure. In this Letter, we show that this novel anion-centered David star structure manifestly breaks inversion symmetry, resulting in flat bands with pronounced Rashba spin-orbit couplings. These distinctive features unlock novel possibilities and functionalities for 1T-TMDs, including the giant spin Hall effect, the emergence of Chern bands, and spin liquid that spontaneously breaks crystalline rotational symmetry. Our findings establish promising avenues for exploring emerging quantum phenomena of monolayer 1T-TMDs with this novel noncentrosymmetric structure.

Giant and tunable photonic spin Hall effect in a parity-time symmetric structure with a Dirac semimetal material

The optical parity-time (PT) symmetry structure can yield unique properties, including periodicity, discreteness, nonlinearity, and so on. However, the component materials in these PT symmetry structures have been primarily restricted by their lack of tunability. Here, by utilizing the external stimulus-dependent optical properties of the Dirac semimetal, we report the theoretical prediction of the large and controllable photonic spin Hall effect in the PT symmetry structure with the slab of the Dirac semimetal. We provide evidence that the PT symmetry structure with the Dirac semimetal exhibits a large spin shift as high as the half of the waist at a certain incident angle, which is the conventionally theoretical upper limit. Due to the exceptional points, the spin shift can be enhanced effectively. Furthermore, we unravel that a small change in the Fermi energy of the Dirac semimetal on the order of 0.01 eV is able to engineer both the magnitude and sign of the spin shift. In particular, there is a transition in the spectrum of the spin shift when we vary the Fermi energy of the Dirac semimetal, where the number of the spin shift peak changes from one to two. Our results reveal the interplay between the light and the PT symmetry structure with the Dirac semimetal, which offers the possibility of developing Dirac semimetal-based spin-dependent photonic devices.

Wave-Guided Surface Plasmonic Resonance Induced Giant and Tunable Photonic Spin Hall Effect with Polarization Mode Control

Wave-Guided Surface Plasmonic Resonance Induced Giant and Tunable Photonic Spin Hall Effect with Polarization Mode Control

Strong polarization-dependent photonic bandgap and giant photonic spin Hall effect in a one-dimensional photonic crystal entirely composed of all-dielectric metamaterials

In conventional one-dimensional (1-D) photonic crystals (PhCs) consisting of isotropic dielectrics, photonic bandgaps (PBGs) exhibit weak polarization-dependent property since the propagating phase of the isotropic dielectric film is polarization-independent. The weak polarization-dependent property of PBGs intensively impedes the potential application of 1-D PhCs in the photonic spin Hall effect (PSHE). Herein, we investigate the polarization-dependent property of PBGs in a class of 1-D PhCs entirely consisting of all-dielectric elliptical metamaterials (EMMs) called all-EMM 1-D PhCs. Driven by the combination of 1-D PhCs and all-dielectric EMMs, strong polarization-dependent PBGs can be realized. Then, we exploit the strong polarization-dependent PBG to achieve giant PSHE. The enhanced transverse shift of the PSHE reaches the order of 102 μm. Our work not only establishes a bridge between PhCs and all-dielectric metamaterials, but also paves a new route to manipulating polarization of light.

Giant spin Hall effect in AB-stacked MoTe2/WSe2 bilayers.

The spin Hall effect (SHE), in which an electrical current generates a transverse spin current, plays an important role in spintronics for the generation and manipulation of spin-polarized electrons. The phenomenon originates from spin-orbit coupling. In general, stronger spin-orbit coupling favours larger SHEs but shorter spin relaxation times and diffusion lengths. However, correlated magnetic materials often do not support large SHEs. Achieving large SHEs, long-range spin transport and magnetism simultaneously in a single material is attractive for spintronics applications but has remained a challenge. Here we demonstrate a giant intrinsic SHE coexisting with ferromagnetism in AB-stacked MoTe2/WSe2 moiré bilayers by direct magneto-optical imaging. Under moderate electrical currents with density <1 A m-1, we observe spin accumulation on transverse sample edges that nearly saturates the spin density. We also demonstrate long-range spin Hall transport and efficient non-local spin accumulation that is limited only by the device size (about 10 µm). The gate dependence shows that the giant SHE occurs only near the interaction-driven Chern insulating state. At low temperatures, it emerges after the quantum anomalous Hall breakdown. Our results demonstrate moiré engineering of Berry curvature and electronic correlation for potential spintronics applications.

High temperature spin Hall effect in topological insulator

Applications of spin–orbit torque (SOT) spintronic devices to automobile or space vehicles require a spin Hall material with high performance at high temperature (&amp;gt;120 °C). However, the spin Hall effect has been studied so far in many materials mostly from cryogenic to room temperature. Here, we studied the spin Hall effect in BiSb topological insulator up to 125 °C. Although the effective spin Hall angle θSHeff of BiSb monotonically decreases with increasing temperature, BiSb maintains a large θSHeff of 4.9 even at 125 °C, demonstrating the capability of BiSb for high temperature applications. Furthermore, the temperature-dependence of the spin Hall conductivity indicates that the topological surface states are the origin of the giant spin Hall effect in BiSb.

Resonant spin Hall effect of light in random photonic arrays

It has been recently shown that the coherent component of light propagating in transversally disordered media, the so-called coherent mode, exhibits an optical spin Hall effect (SHE). In non-resonant materials, however, this phenomenon shows up at a spatial scale much larger than the mean free path, making its observation challenging due to the exponential attenuation of the coherent mode. Here, we show that in disordered photonic arrays exhibiting Mie resonances, the SHE on the contrary appears at a scale smaller than the mean free path if one operates in the close vicinity of the lowest transverse-magnetic resonance of the array. In combination with a weak measurement, this gives rise to a giant SHE that should be observable in optically-thin media. Furthermore, we show that by additionally exploiting the cooperative emission of a flash of light following the abrupt extinction of the incoming beam, one can achieve a time-dependent SHE, observable at large optical thickness as well.

Giant photonic spin Hall effect empowered by polarization-dependent quasibound states in the continuum in compound grating waveguide structures

The photonic spin Hall effect (PSHE) plays an important role in both fundamental science and precision metrology. In this paper, we theoretically propose a polarization-dependent bound state in the continuum (BIC) in a compound grating waveguide structure based on the selectable guided resonance at near-infrared wavelengths. Empowered by the unique resonant property and polarization-dependent property of the quasi-BIC, the transverse shift of the PSHE can be intensively enhanced to the order of hundreds of micrometers. Besides, the enhancement of the transverse shift of the PSHE is robust against the geometric parameters. Our work not only provides an all-dielectric platform to achieve giant PSHE, but also offers a viable approach to design high-performance PSHE-based optical devices.

Giant and tunable Rashba spin splitting and quantum spin Hall effect in H-Pb-Cl

Rashba spin splitting and quantum spin Hall effect have attracted enormous interest due to their great significance in the application of spintronics. According to the first-principles calculation, we propose a two-dimensional hexagonal lattice material H-Pb-Cl, which realizes the coexistence of giant Rashba spin splitting and quantum spin Hall effect. Owing to the break of space inversion symmetry and the existence of intrinsic electric field, H-Pb-Cl has a huge Rashba spin splitting phenomenon (&lt;i&gt;α&lt;/i&gt;&lt;sub&gt;R&lt;/sub&gt; = 3.78 eV·Å), and the Rashba spin splitting of H-Pb-Cl(–16%—16%) can be adjusted by changing the biaxial stress. By analyzing the electronic properties of H-Pb-Cl, we find that H-Pb-Cl has a huge band gap near the Fermi surface (1.31 eV), and the topological invariant &lt;i&gt;Z&lt;/i&gt;&lt;sub&gt;2&lt;/sub&gt; = 1 of the system is caused by the inversion of s-p orbit, which indicates that H-Pb-Cl is a two-dimensional topological insulator with a huge topological band gap, and the gap is large enough to observe the topological edge states at room temperature. In addition, we further consider the effect of BN and graphane substrates on the topological band gap of H-Pb-Cl by using the H-Pb-Cl (111)-(1×1) /BN (111)-(2×2) and H-Pb-Cl(1×1)/ graphane (2×2) system, and find that the lattice mismatch between H-Pb-Cl (5.395 Å) and BN (2.615 Å) and between H-Pb-Cl (5.395 Å) and graphane (2.575 Å) are about 3% and 4.5%, respectively. According to our calculation results, H-Pb-Cl still retains the properties of topological insulator under the effect of spin orbit coupling, and is not affected by BN nor graphane. Our results show that the nontrivial topological band gap of H-Pb-Cl can be well preserved under both biaxial stress effect and substrate effect. In addition, H-Pb-Cl can well retain the nontrivial topological band gap under the stress of –16%–16%, and thus there are many kinds of substrate materials used to synthesize this material, which is very helpful in successfully realizing preparation experimentally. Our research provides a promising candidate material for exploring and realizing the coexistence of Rashba spin splitting and quantum spin Hall effect. And the coexistence of giant Rashba spin splitting and quantum spin Hall effect greatly broadens the scope of potential applications of H-Pb-Cl in the field of spintronic devices.

Giant photonic spin Hall effect induced by hyperbolic shear polaritons.

Recently, broken symmetry within crystals has been attracting tremendous research interest since it can be utilized to effectively manipulate the propagation of photons. In particular, low-symmetry Bravais crystals can support hyperbolic shear polaritons (HShPs), holding great promise for technological upgrading in the emerging research area of spinoptics. Herein, an Otto-type multilayer structure consisting of a KRS5 prism, a sensing medium, and monoclinic β-Ga2O3 crystals is designed to ameliorate the photonic spin Hall effect (PSHE). The surface of β-Ga2O3 is the monoclinic (010) plane (x-y plane). We show that giant spin Hall shifts with three (or two) orders of magnitude of the incident wavelength can be obtained in the in-plane (or transverse) directions. The azimuthal dispersions of photonic spin Hall shifts present non-mirror-symmetric patterns upon tuning the rotation angle of β-Ga2O3 around the z-axis in the plane. All of these exotic optical properties are closely correlated with the broken crystal lattice symmetry and the incurred excitation of HShPs in monoclinic β-Ga2O3 crystals. By virtue of the remarkably enhanced PSHE, our proposed Otto-type multilayer structure shows a superior biosensing performance in which the maximum sensitivity is two orders of magnitude larger than that of previously reported PSHE biosensors based on two-dimensional materials. In addition, the optimized physical and structural parameters including the incident angle, excitation wavelength, azimuth angle and doping concentration of β-Ga2O3, thickness and refractive index of sensing medium are also investigated and presented. This work unequivocally confirms the strong influence of crystal symmetry on the PSHE, providing important insights into understanding the rich modulation of spin-orbit interactions of light via shear polaritons and therefore facilitating potential applications in photoelectronic devices.

Highly efficient spin current source using BiSb topological insulator/NiO bilayers

BiSb is a topological insulator with both giant spin Hall effect and high electrical conductivity, which are important for ultralow power spin–orbit-torque magnetoresistive random access memory. However, when a ferromagnetic (FM) thin film is deposited on top of BiSb, large surface roughness and diffusion of Sb out of the BiSb layer into the FM layer results in a much smaller effective spin Hall angle In this work, we show that by inserting a NiO layer between BiSb and Co, we can significantly improve of BiSb and induce perpendicular magnetic anisotropy at the NiO/Co interface. We obtained a large = 10.3 for the BiSb bottom layer at the NiO layer thickness of 3 nm, which is comparable to the best of BiSb top layer studied so far. Our study shows that BiSb/NiO bilayers are promising for integration of BiSb to SOT-MRAM.

Giant longitudinal spin Hall effect for elliptically polarized light under surface plasmon resonance

We propose a novel and simple method for obtaining the giant longitudinal spin Hall effect (SHE) of the reflected light beam when the elliptically polarized light (instead of the linearly polarized light) at the telecommunication wavelength is obliquely incident on a prism–sodium interface excited by surface plasmon resonance. By introducing the spatially averaged Stokes parameter for a non-uniformly polarized reflected light field, understanding the generation mechanism of the giant longitudinal SHE from a new perspective is realized. The giant longitudinal SHE under the elliptically polarized light reaches 60.28 μm by the optimal parameter setup, and the spin splitting direction of the SHE can be switched by adjusting the amplitude ratio angle and phase difference of the incident elliptically polarized light. These findings open the way for the precise measurement of the ellipticity of the elliptically polarized light and the design of novel fiber-optic devices.

Coexistence of giant Rashba spin splitting and quantum spin Hall effect in H–Pb–F

Rashba spin splitting (RSS) and quantum spin Hall effect (QSHE) have attracted enormous interest due to their great significance in the application of spintronics. In this work, we theoretically proposed a new two-dimensional (2D) material H–Pb–F with coexistence of giant RSS and quantum spin Hall effec by using the ab initio calculations. Our results show that H–Pb–F possesses giant RSS (1.21 eV⋅Å) and the RSS can be tuned up to 4.16 eV⋅Å by in-plane biaxial strain, which is a huge value among 2D materials. Furthermore, we also noticed that H–Pb–F is a 2D topological insulator (TI) duo to the strong spin–orbit coupling (SOC) interaction, and the large topological gap is up to 1.35 eV, which is large enough for for the observation of topological edge states at room temperature. The coexistence of giant RSS and quantum spin Hall effect greatly broadens the potential application of H–Pb–F in the field of spintronic devices.

Giant spin Hall effect in half-Heusler alloy topological semimetal YPtBi grown at low temperature

Half-Heusler alloy topological semimetal YPtBi is a promising candidate for an efficient spin source material having both large spin Hall angle θSH and high thermal stability. However, high-quality YPtBi thin films with low bulk carrier density are usually grown at 600 °C, which exceeds the limitation of 400 °C for back end of line (BEOL) process. Here, we investigate the crystallinity and spin Hall effect of YPtBi thin films grown at lower growth temperature down to 300 °C. Although both effective spin Hall angle and spin Hall conductivity degraded with lowering the growth temperature to 300 °C due to degradation of the interfacial spin transparency, they were recovered by reducing the sputtering Ar gas pressure. We achieved a giant θSH up to 7.8 and demonstrated efficient spin–orbit torque magnetization switching by ultralow current density of ∼105 A/cm2 in YPtBi grown at 300 °C with the Ar gas pressure of 1 Pa. Our results provide the recipe to achieve giant θSH in YPtBi grown at lower growth temperature suitable for BEOL process.

Giant Photonic Spin Hall Effect by Anisotropic Band in Photonic Crystal Slabs

When a paraxial light beam is reflected from/ transmitted through an optical element with rotation symmetry, a tiny small incident angle can arise wave-vector-varying Pancharatnam-Berry (PB) phases, resulting in high-performance photonic spin Hall effect (PSHE). Differently, here we investigate the PSHE in photonic crystal slabs of square lattices constructed with air holes, and demonstrate that the C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4v</sub> symmetry of the slabs enables giant PSHE in both isotropic and anisotropic band structures with a small incident angle. The guided-mode resonances of the subwavelength-thickness slab enhance the PSHE, allowing the spin separation to exceed the incident beam waist. Via changing the incident angle, wavelength and even the beam waist, the spin separation can be adjusted in a wide range, which makes our proposal more flexible in manipulation of spin photons.

Giant photonic spin Hall effect in bilayer borophene metasurfaces.

We investigate theoretically the photonic spin Hall effect (PSHE) in bilayer borophene metasurfaces. Based on the combined effect of the Fabry-Perot resonance of the bilayer system and the resonant interaction of individual meta-atoms in borophene metasurface which lead to the topological transition, it is found that there exist giant PSHE shifts of the transmitted beams which can be flexibly regulated by adjusting the twist angle of metasurface bilayers, incident angle, spacer refractive index and spacer thickness. Near the topological transition of borophene metasurface the magnitude of PHSE shifts in bilayer borophene metasurfaces is generally on the order of tens of wavelengths and even on the order of hundreds of wavelengths near the epsilon-near-zero (ENZ) regions. The manipulation frequency range of the large PSHE shifts can reach hundreds of terahertz or even picohertz through adjusting the ribbon width of borophene metasurface or the electron density for borophene. It is found that in bilayer borophene metasurfaces there exist the ultrahigh sensitivity of the PSHE shifts to spacer refractive index, which can be applied to design the refractive index sensors with high performance.

Wide-angle giant photonic spin Hall effect

The photonic spin Hall effect is a manifestation of the spin-orbit interaction of light and can be measured by a transverse shift $\ensuremath{\delta}$ of photons with opposite spins. The precise measurement of transverse shifts can enable many spin-related applications, such as precise metrology and optical sensing. However, this transverse shift is generally small (i.e., $\ensuremath{\delta}/\ensuremath{\lambda}&lt;{10}^{\ensuremath{-}1}$, where $\ensuremath{\lambda}$ is the wavelength), which impedes its precise measurement. To date, proposals to generate a giant spin Hall effect (namely, with $\ensuremath{\delta}/\ensuremath{\lambda}&gt;{10}^{2}$) have severe limitations, particularly its occurrence only over a narrow angular cone (with a width of $\mathrm{\ensuremath{\Delta}}\ensuremath{\theta}&lt;{1}^{\ensuremath{\circ}}$). Here we propose a universal scheme to realize the wide-angle giant photonic spin Hall effect with $\mathrm{\ensuremath{\Delta}}\ensuremath{\theta}&gt;{70}^{\ensuremath{\circ}}$ by exploiting the interface between free space and uniaxial epsilon-near-zero media. The underlying mechanism is ascribed to the almost-perfect polarization splitting between $s$ and $p$ polarized waves at the designed interface. Remarkably, this almost-perfect polarization splitting does not resort to the interference effect and is insensitive to the incident angle, which then gives rise to the wide-angle giant photonic spin Hall effect.

Polarization manipulation of giant photonic spin Hall effect using wave-guiding effect

The enhanced photonic spin Hall effect was previously possible only for the horizontal polarization (H-polarized) in plasmonic systems. The wave-guiding surface plasmonic resonance (SPR) effect is used to report a giant photonic spin Hall effect (G-PSHE) of reflected light for horizontal and vertical polarized waves. This novel work investigated the polarization-manipulated G-PSHE in the modified Kretschmann configuration with an additional glass dielectric thin wave-guiding layer. The ultrathin gold layer and an additional dielectric wave-guiding layer are responsible for achieving millimeter-scale (more than 2 mm to submillimeter) G-PSHE. With this novel approach, polarization manipulation is achieved by employing wave-guiding and the SPR effect. Using a finite element method based simulation study, the impact of an additional thin dielectric wave-guiding layer on G-PSHE is investigated. This study enables the potential application of both horizontal and vertical polarization-based quantum devices and sensors for which light spin plays a pivotal role.

Spin Orbit Torque-Assisted Magnetic Tunnel Junction-Based Hardware Trojan

With the advancement of beyond-CMOS devices to keep Moore’s law alive, several emerging devices have found application in a wide range of applications. Spintronic devices offer low power, non-volatility, inherent spatial and temporal randomness, simplicity of integration with a silicon substrate, etc. This makes them a potential candidate for next-generation hardware options. This work explores the giant spin Hall effect (GSHE)-driven spin-orbit torque (SOT) magnetic tunnel junction (MTJ) as a potential candidate for creating an externally triggered hardware Trojan and insertion into logic-locked hardware security considering the effect of process and temperature variations.