Intrinsic Spin Hall Effect Research Articles

Memcapacitors and Memristor Characteristics of ISGE-SOT and SHE-SOT Gain-Driven MoS2:Er Ferromagnets.

The enhancement of the spin-orbit torque (SOT) effect through the integration of intrinsic inverse spin galvanic effect spin-orbit torque and spin Hall effect spin-orbit torque is fundamentally dependent on the structural and material properties of the ferromagnets. Consequently, the synthesis of ferromagnets with superior structural integrity and material characteristics is of paramount importance. In this study, a gas-liquid chemical reaction, in conjunction with ultrasonic crushing, was employed to synthesize few-layer MoS2:Er nanosheets. X-ray diffraction, X-ray photoelectron spectroscopy, and energy-dispersive spectroscopy analyses confirm the successful substitution of Mo4+ by Er3+ through doping within the MoS2 lattice. Vibrating sample magnetometry and MT measurements indicate that MoS2:Er exhibits room-temperature ferromagnetism (RTFM), with the underlying mechanism elucidated through first-principles calculations. Furthermore, the unique electron density of states at the Fermi level suggests the presence of ferromagnetism in MoS2:Er. A wedge-shaped Pt/MoS2:Er/Au structure was fabricated and subsequently evaluated for current-induced SOT switching, as well as for its memcapacitor and memristor characteristics. The precession of a magnetic moment in three-dimensional space was successfully simulated by solving the Landau-Lifshitz-Gilbert-Slonczewski equation using the Mumax.

Intrinsic anomalous, spin and valley Hall effects in ’ex-so-tic’ van-der-Waals structures

We consider the anomalous, spin, valley, and valley spin Hall effects in a pristine graphene-based van-der-Waals (vdW) heterostructure consisting of a bilayer graphene (BLG) sandwiched between a semiconducting van-der-Waals material with strong spin-orbit coupling (e.g., WS2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {WS}_2$$\\end{document}) and a ferromagnetic insulating vdW material (e.g. Cr2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {Cr}_2$$\\end{document}Ge2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {Ge}_2$$\\end{document}Te6\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {Te}_6$$\\end{document}). Due to the exchange proximity effect from one side and spin-orbit proximity effect from the other side of graphene, such a structure is referred to as graphene based ’ex-so-tic’ structure. First, we derive an effective Hamiltonian describing the low-energy states of the structure. Then, using the Green’s function formalism, we obtain analytical results for the Hall conductivities as a function of the Fermi energy and gate voltage. For specific values of these parameters, we find a quantized valley Hall conductivity.

Spin Hall effect in doped ferroelectric HfO2

The spin Hall effect (SHE) enables charge-to-spin conversion by electrical means and is promising for spintronic applications. Here, we report on the intrinsic spin Hall effect in the prototypical ferroelectric material HfO2 with charge doping using density functional theory calculations and theoretical analysis. We show that ferroelectric displacements are insensitive to charge doping and are sustained up to a large doping concentration of 0.4 electrons or holes per unit cell volume. In addition, the large spin Hall conductivity in the vicinity of the band edges is well preserved. Intriguingly, we demonstrate the giant spin Hall efficiency characterized by the sizable spin Hall angle of ∼0.1 in doped HfO2. These results add unexplored functionality to ferroelectric HfO2 and open opportunities for potential device applications.

Intrinsic spin Hall effect in topological semimetals with single Dirac nodal ring

Intrinsic spin Hall effect in topological semimetals with single Dirac nodal ring

Enhanced orbital torque efficiency in nonequilibrium Ru50Mo50(0001) alloy epitaxial thin films

Epitaxial thin films of fully nonequilibrium hcp-Ru50Mo50(0001) nanoalloys were prepared as a chemically disordered alloy, in which the intrinsic spin Hall effect is expected to be negligible. Structural analyses confirmed the epitaxial growth and atomic scale alloying of the films. In contrast to a tiny torque efficiency (ξDL) of ∼0.4% for Ru50Mo50/CoFeB, the ξDL for the Ru50Mo50/Ni heterostructure reached ∼30% with a long-range relaxation length. The apparent dependence of ξDL on the ferromagnetic layer can be attributed to the orbital Hall effect (OHE). Interestingly, a smaller ξDL was observed for Ru/Ni, suggesting that the nonequilibrium Ru50Mo50 enhances its OHE. Furthermore, the enhanced ξDL is maintained by inserting a Ru layer between the Ru50Mo50 and Ni layers, showing orbital transport through Ru. This finding illustrates potential applications of nonequilibrium nanoalloy films in spin orbitronics and contributes to getting insights into the understanding of the interrelationships between nanostructures and orbital transport properties.

Tuning the intrinsic spin Hall effect by charge density wave order in topological kagome metals

Tuning the intrinsic spin Hall effect by charge density wave order in topological kagome metals

Tuning Intrinsic Spin Hall Effect in Platinum/Ferrimagnetic Insulator Heterostructure in Moderately Dirty Regime.

Studying the mechanisms of the spin Hall effect (SHE) is essential for the fundamental understanding of spintronic physics. By now, despite the intensive studies of SHE on heavy metal (HM)/metallic magnet heterostructures, the SHE on HM/ferrimagnetic insulator (FMI) heterostructures still remains elusive. Here, we study the mechanism of SHE in the Pt/Tm3Fe5O12 (TmIG) heterostructure. We first tune the crystallinity and resistivity of Pt by an annealing method, and then study the spin-orbit torque (SOT) in the tuned-Pt/TmIG devices. The SOT generation efficiency per unit electric field and spin Hall angle were obtained, which are insensitive to the annealing temperature. We further demonstrate that the intrinsic contribution in the moderately dirty regime is responsible for the SHE in our Pt/TmIG bilayer. Our study provides an important piece of information for the SHE in FMI-based spintronic physics.

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.

Efficient charge to spin conversion in iridium oxide thin films

Many 5d transition metal oxides have a unique electronic structure, where the density of states near the Fermi level is dominated by only 5d electrons with strong spin–orbit coupling. IrO2, a Dirac nodal line semi-metal, is the simplest of these oxides. The presence of 5d electrons and gap opening of Dirac nodal lines via strong spin–orbit coupling allows for the hybridization of the 5d electrons of the oxide with the itinerant d electrons of a ferromagnet, while simultaneously increasing the intrinsic spin Hall effect. We report large charge-to-spin conversion in thin films of this material using spin-torque ferromagnetic resonance experiments. By independently performing line shape analysis and linewidth modulation experiments, we conclusively determine the spin Hall angle of optimized IrO2 films to be ∼8 times larger than that of Pt.

Composite Spin Hall Conductivity from Non-Collinear Antiferromagnetic Order.

Non-collinear antiferromagnets (AFMs) are an exciting new platform for studying intrinsic spin Hall effects (SHEs), phenomena that arise from the materials' band structure, Berry phase curvature, and linear response to an external electric field. In contrast to conventional SHE materials, symmetry analysis of non-collinear antiferromagnets does not forbid non-zero longitudinal and out-of-plane spin currents with polarization and predicts an anisotropy with current orientation to the magnetic lattice. Here, multi-component out-of-plane spin Hall conductivities are reported in L12 -ordered antiferromagnetic PtMn3 thin films that are uniquely generated in the non-collinear state. The maximum spin torque efficiencies (ξ = JS /Je ≈ 0.3) are significantly larger than in Pt (ξ ≈ 0.1). Additionally, the spin Hall conductivities in the non-collinear state exhibit the predicted orientation-dependent anisotropy, opening the possibility for new devices with selectable spin polarization. This work demonstrates symmetry control through the magnetic lattice as a pathway to tailored functionality in magnetoelectronic systems.

Intrinsic orbital and spin Hall effect in bismuth semimetal

We investigate the intrinsic orbital Hall conductivity (OHC) and spin Hall conductivity (SHC) in a bismuth semimetal, by employing an $sp$-orbital tight-binding model. We report a notable difference between the anisotropy of OHC and SHC whose orbital and spin polarizations lie within the basal plane. We do not observe a substantial correlation between the orbital and spin Berry curvatures with spin-orbit coupling (SOC) at the Fermi energy, disproving the correlation between OHC and SHC in a strong SOC regime. We argue the huge SHC in a Bi semimetal is attributed to its gigantic SOC which strongly affects the hybridization of the $p$ orbitals, despite its relatively small magnitude of OHC. We hope the distinct anisotropy of OHC and SHC provides a feasible means to differentiate between the two effects in experiments.

Topological superconductivity and large spin Hall effect in the kagome family Ti6X4 (X = Bi, Sb, Pb, Tl, and In)

Topological superconductors (TSC) become a focus of research due to the accompanying Majorana fermions. However, the reported TSC are extremely rare. Recent experiments reported kagome TSC AV3Sb5 (A= K, Rb, and Cs) exhibit unique superconductivity, topological surface states (TSS), and Majorana bound states. More recently, the first titanium-based kagome superconductor CsTi3Bi5 with nontrivial topology was successfully synthesized as a perspective TSC. Given that Cs contributes little to electronic structures of CsTi3Bi5 and binary compounds may be easier to be synthesized, here, by first-principle calculations, we predict five stable nonmagnetic kagome compounds Ti6X4 (X= Bi, Sb, Pb, Tl, and In) which exhibit superconductivity with critical temperature Tc= 3.8 K 5.1 K, nontrivial band topology, and TSS close to the Fermi level. Additionally, large intrinsic spin Hall effect is obtained in Ti6X4, which is caused by gapped Dirac nodal lines due to a strong spin-orbit coupling. This work offers new platforms for TSC and spintronic devices.

Strong Spin-Orbit Torque Induced by the Intrinsic Spin Hall Effect in Cr1−xPtx

We report on a spin-orbit torque study of the spin current generation in Cr1-xPtx alloy, using the light 3d ferromagnetic Co as the spin current detector. We find that the dampinglike spin-orbit torque of Cr1-xPtx/Co bilayers can be enhanced by tuning the Cr concentration in the Cr1-xPtx layer, with a maximal value of 0.31 at the optimal composition of Cr0.2Pt0.8. We find that the spin current generation in the Cr1-xPtx alloy can be fully understood by the characteristic trade-off between the intrinsic spin Hall conductivity of Pt and the carrier lifetime in the dirty limit. We find no evidence for the spin current generation by other mechanisms in this material, revealing that the role of Cr is found to be simply the same as other metals and oxides in previous studies. This work also establishes the low-resistivity Cr0.2Pt0.8 as an energy-efficient spin-orbit torque provider for magnetic memory and computing technologies.

Perpendicular Magnetization Switching Driven by Spin‐Orbit Torque for Artificial Synapses in Epitaxial Pt‐Based Multilayers

AbstractPerpendicular magnetization switching driven by spin‐orbit torque (SOT) exhibits nonvolatility and adjustability, which has great potential applications in magnetic random‐access memory and neuromorphic computing. In this work, the SOT efficiency in the Pt (001)/NiFe (Py) and Pt (111)/Py bilayers is first investigated, where the single crystal Pt films and polycrystalline Py films are grown by molecular beam epitaxy and magnetron sputtering, respectively. The (001)‐oriented Pt sample shows a larger SOT efficiency than that of the (111)‐oriented one, which is mainly attributed to the facet‐dependent intrinsic spin Hall effect of the Pt layer related to the Berry curvature of the electrical band structure. Then, the epitaxial Pt (001)‐based perpendicularly magnetized multilayers are designed to study the perpendicular magnetization switching driven by SOT. A continuous and stable reversal is successfully achieved, providing a conceivable candidate for reliable and variable imitation of the artificial synapses. The magneto–optical Kerr effect imaging proves that the sustainable change of magnetization state originates from the multiple site domain nucleation and growth in the ferromagnetic layer. This work provides an efficient method to enhance the SOT efficiency, as well as employs the epitaxial thin films in artificial synaptic devices for neuromorphic computing.

Fluctuation contribution to spin Hall effect in superconductors

We theoretically study the contribution of superconducting fluctuation to extrinsic spin Hall effects in two- and three-dimensional electron gas and intrinsic spin Hall effects in two-dimensional electron gas with Rashba-type spin-orbit interaction. The Aslamazov-Larkin, Density-of-States, Maki-Thompson terms have logarithmic divergence $\ln\epsilon$ in the limit $\epsilon=(T- T_{\mathrm{c}})/T_{\mathrm{c}} \rightarrow +0$ in two-dimensional systems for both extrinsic and intrinsic spin Hall effects except the Maki-Thompson terms in extrinsic effect, which are proportional to $(\epsilon-\gamma_\varphi)^{-1}\ln\epsilon$ with a cutoff $\gamma_\varphi$ in two-dimensional systems. We found that the fluctuation effects on the extrinsic spin Hall effect have an opposite sign to that in the normal state, while those on the intrinsic spin Hall effect have the same sign.

First-principles theory of intrinsic spin and orbital Hall and Nernst effects in metallic monoatomic crystals

The generation of spin and orbital currents is of crucial importance in the field of spin-orbitronics. In this work, using relativistic density functional theory and the Kubo linear-response formalism, we systematically investigate the spin Hall and orbital Hall effects for 40 monoatomic metals. The spin Hall conductivity and orbital Hall conductivity (OHC) are computed as a function of the electrochemical potential and the influence of the spin-orbit interaction strength is also investigated. Our calculations predict a rather small OHC in $sp$ metals, but a much larger OHC in $d$-band metals, with maximum values $[\ensuremath{\sim}8000(\ensuremath{\hbar}/e)\phantom{\rule{0.28em}{0ex}}{(\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\mathrm{cm})}^{\ensuremath{-}1}]$ near the middle of the $d$ series. Using the Mott formula, we evaluate the thermal counterparts of the spin and orbital Hall effects, the spin Nernst effect (SNE), and the orbital Nernst effect (ONE). We find that the as-yet unobserved ONE is significantly larger $(\ensuremath{\sim}10\ifmmode\times\else\texttimes\fi{})$ than the SNE and has maximum values for group 10 elements (Ni, Pd, and Pt). Our work provides a broad overview of electrically and thermally induced spin and orbital transport in monoatomic metals.

Giant intrinsic spin Hall effect in layered material Pt2B

Spin Hall effect (SHE) is highly promising for future spintronic applications. Using ab initio calculations , we predict that the hexagonal layered material Pt 2 B exhibits a giant intrinsic SHE with an intrinsic spin Hall conductivity (SHC) of 2159 ( ħ / e ) S/cm, which can reach its maximum value of 2274 ( ħ / e ) S/cm at 0.04 eV above the intrinsic Fermi level. The large SHC mainly comes from the contributions of the two occupied bands below the Fermi level, and the energy difference between the occupied and unoccupied states determines the energy position of the maximal SHC. Pt 2 B’s spin Hall angle (SHA) is of the same order as pure metal Pt. Our finds suggest that Pt 2 B is a fascinating material for producing pure spin current. • Pt 2 B could be a ideal system for achieving large SHC. It has an intrinsic SHC σ x y z as large as 2159 ( ħ / e ) S/cm. • The large SHC mainly come from the contribution of the two occupied bands below the Fermi level, and the energy difference between occupied and unoccupied states determines the energy position of maximal SHC. • The bands around the Fermi level do not have the SOC-induced anti-cross. Therefore, the mechanism of the large SHC of Pt 2 B is different from many previous reported materials.

Geometric origin of intrinsic spin hall effect in an inhomogeneous electric field

In recent years, the spin Hall effect has received great attention because of its potential application in spintronics and quantum information processing and storage. However, this effect is usually studied under the external homogeneous electric field. Understanding how the inhomogeneous electric field affects the spin Hall effect is still lacking. Here, we investigate a two-dimensional two-band time-reversal symmetric system and give an expression for the intrinsic spin Hall conductivity in the presence of the inhomogeneous electric field, which is shown to be expressed through the geometric quantities: quantum metric and interband Berry connection. We show that for Rashba and Dresselhaus systems, the inhomogeneous intrinsic spin Hall conductivity can be tuned with the Fermi energy. On the other hand, when people get physical intuition on transport phenomena from the wave packet, one issue appears. It is shown that the conductivity obtained from the conventional wave packet approach cannot be fully consistent with the one predicted by the Kubo-Greenwood formula. Here, we attempt to solve this problem.

Large intrinsic spin Hall conductivity and spin Hall angle in the nodal-line semimetals ThAl2 and ThGa2

The intrinsic spin Hall effect and topological properties of ${\mathrm{ThAl}}_{2}$ and ${\mathrm{ThGa}}_{2}$ have been investigated based on first-principles electronic structure calculations. The band structures calculated without the spin-orbital coupling (SOC) show that both ${\mathrm{ThAl}}_{2}$ and ${\mathrm{ThGa}}_{2}$ host multiple nodal lines near the Fermi level. Once the SOC is taken into account, these nodal lines are gapped and huge spin Berry curvatures can be generated. As a result, giant spin Hall conductances of ${\mathrm{ThAl}}_{2}$ and ${\mathrm{ThGa}}_{2}$ are induced around the Fermi level. Moreover, large spin Hall angles can be achieved due to the giant spin Hall conductance and the small electric conductivity. Our work indicates that ${\mathrm{ThAl}}_{2}$ and ${\mathrm{ThGa}}_{2}$ not only provide an ideal platform for exploring the interplay between spin Hall effect and topological property, but also have promising applications in spin-orbitronic devices.

Trigonal multivalent polonium monolayers with intrinsic quantum spin Hall effects

Two-dimensional (2D) topological insulators, a type of the extraordinary quantum electronic states, have attracted considerable interest due to their unique electronic properties and promising potential applications. Recently, the successful fabrication of 2D Te monolayers (i.e. tellurene) in experiments (Zhu et al., Phys Rev Lett 119:106101, 2017) has promoted researches on the group-VI monolayer materials. With first-principles calculations and tight-binding (TB) method, we investigate the structures and electronic states of 2D polonium (poloniumene), in which Po is a congener of Te. The poloniumene is found to have the tendency of forming a three-atomic-layer 1 T-MoS2-like structure (called trigonal poloniumene), namely, the central-layer Po atoms behave metal-like, while the two-outer-layer Po atoms are semiconductor-like. This unique multivalent behavior of the Po atoms is conducive to the structural stability of the monolayer, which is found to be an intrinsic quantum spin Hall insulator with a large band gap. The nontrivial topology originates from the p_{x,y} - p_{z} band inversion, which can be understood based on a built TB model. The poloniumene with different congener elements doped is also explored. Our results provide a thorough understanding of structures and electronic states of 2D polonium-related materials.