Inverse Rashba-Edelstein Effect Research Articles

Emerging Nonlinear Photocurrents in Lead Halide Perovskites for Spintronics.

Lead halide perovskites (LHPs) containing organic parts are emerging optoelectronic materials with a wide range of applications thanks to their high optical absorption, carrier mobility, and easy preparation methods. They possess spin-dependent properties, such as strong spin-orbit coupling (SOC), and are promising for spintronics. The Rashba effect in LHPs can be manipulated by a magnetic field and a polarized light field. Considering the surfaces and interfaces of LHPs, light polarization-dependent optoelectronics of LHPs has attracted attention, especially in terms of spin-dependent photocurrents (SDPs). Currently, there are intense efforts being made in the identification and separation of SDPs and spin-to-charge interconversion in LHP. Here, we provide a comprehensive review of second-order nonlinear photocurrents in LHP in regard to spintronics. First, a detailed background on Rashba SOC and its related effects (including the inverse Rashba-Edelstein effect) is given. Subsequently, nonlinear photo-induced effects leading to SDPs are presented. Then, SDPs due to the photo-induced inverse spin Hall effect and the circular photogalvanic effect, together with photocurrent due to the photon drag effect, are compared. This is followed by the main focus of nonlinear photocurrents in LHPs containing organic parts, starting from fundamentals related to spin-dependent optoelectronics. Finally, we conclude with a brief summary and future prospects.

Atomic-Layer Controlled Transition from Inverse Rashba-Edelstein Effect to Inverse Spin Hall Effect in 2D PtSe2 Probed by THz Spintronic Emission.

2D materials, such as transition metal dichalcogenides, are ideal platforms for spin-to-charge conversion (SCC) as they possess strong spin-orbit coupling (SOC), reduced dimensionality and crystal symmetries as well as tuneable band structure, compared to metallic structures. Moreover, SCC can be tuned with the number of layers, electric field, or strain. Here, SCC in epitaxially grown 2D PtSe2 by THz spintronic emission is studied since its 1T crystal symmetry and strong SOC favor SCC. High quality of as-grown PtSe2 layers is demonstrated, followed by in situ ferromagnet deposition by sputtering that leaves the PtSe2 unaffected, resulting in well-defined clean interfaces as evidenced with extensive characterization. Through this atomic growth control and using THz spintronic emission, the unique thickness-dependent electronic structure of PtSe2 allows the control of SCC. Indeed, the transition from the inverse Rashba-Edelstein effect (IREE) in 1-3 monolayers (ML) to the inverse spin Hall effect (ISHE) in multilayers (>3 ML) of PtSe2 enabling the extraction of the perpendicular spin diffusion length and relative strength of IREE and ISHE is demonstrated. This band structure flexibility makes PtSe2 an ideal candidate to explore the underlying mechanisms and engineering of the SCC as well as for the development of tuneable THz spintronicemitters.

Surface-state mediated spin-to-charge conversion in Sb films via bilateral spin current injection

The spin-to-charge conversion phenomenon is investigated in a trilayer structure consisting of Co(12 nm)/Sb(t)/Py(12 nm), where the thickness t of the antimony layer is varied. Using the spin-pumping technique, a pure spin current is injected from both FM layers into the middle layer, the DC voltage is then measured. We observe a spin-to-charge mechanism in the Sb layer that exhibits striking similarities to the inverse Rashba–Edelstein effect (IREE), driven by surface states.

Theory of inverse Rashba-Edelstein effect induced by spin pumping into a two-dimensional electron gas

Theory of inverse Rashba-Edelstein effect induced by spin pumping into a two-dimensional electron gas

Spin-to-charge conversion origin in graphene on ferromagnetic substrate revealed: Rashba effects at Dirac point

Spin-to-charge current conversion (SCC) by inverse Rashba Edelstein effect (IREE) has been recently observed by spin-pumping experiment in single layer graphene (SLG) placed on ferromagnetic substrate composed mostly of Ni. However, a prior angle-resolved photoemission spectroscopy (ARPES) shows a negligible Rashba splitting at Γ−M, unsupportive of SCC by IREE. In this work, using density functional theory with spin-orbit coupling (DFT + SOC) calculations, we obtained the Rashba-type spin-resolved bandstructure on relevant symmetric k-points of SLG on Ni(111). We found no Rashba splitting at Γ−M confirming ARPES, however, we discovered considerable Rashba splittings in the dispersions along M−K−M, that is, involving the Dirac point, paving the way for SCC by IREE. Thus, for the first time, this work has reconciled the above seemingly contradicting spin-pumping and ARPES experiments, revealed the physical and magnetic origin of SCC by IREE and proposed means to increase the SCC coefficient without the use of heavy precious metals.

Tunable Spin Seebeck Thermopower in Nonlocal Perovskite MAPbBr3‐Based Structure

AbstractRecently organic–inorganic hybrid perovskite (OIHP) has risen suddenly to become a superstar for spintronic applications. Fundamental understanding of its spin properties is of great importance for future advances of its applications in spin‐optoelectronic devices. In this work, the authors pioneer modulation of the spin Seebeck thermopower (SSTP) in a Pt/MAPbBr3/NiFe nonlocal structure via longitudinal spin Seebeck effect measurements. They unravel the effective magnon injection into the perovskite film from the NiFe layer, and the tunability of SSTP in this structure is easily realized through the optimization of morphology and component engineering of the OIHP film. First, upon biasing samples with a magnetic flux density during the preparation process, a high‐quality OIHP film can be obtained, in which the spin scattering can be reduced leading to the SSTP enhancement. Second, by doping Cr into the OIHP lattice, the increased magnetic moment density and the additional in‐plane inverse Rashba–Edelstein effect synergistically improve spin accumulation in the Pt layer and thus tune its SSTP. Unveiling those phenomena is important to understanding magnon transport in the OIHP interlayer, which is instructive for designing magnonic devices based on OIHP film.

Inverse Orbital Torque via Spin-Orbital Intertwined States

Spin torque induced by orbital current has become of great interest, as it allows the use of lighter elements in the development of advanced spin-orbitronic devices. Meanwhile, the inverse orbital torque (IOT) effect, in which an orbital current creates a charge current, has been difficult to detect. This study uses pumped spin-orbital current in Y${}_{3}$Fe${}_{5}$O${}_{12}$/Pt/CuO${}_{x}$ heterostructures to investigate the IOT effect. Mixed spin-orbital states propagate to the Pt/CuO${}_{x}$ interface and create a much stronger transverse charge current than that created without the CuO${}_{x}$ coating. This inverse orbital Rashba-Edelstein effect can be used to advance applications in spintronics.

Efficient Spin‐to‐Charge Interconversion in Weyl Semimetal TaP at Room Temperature

AbstractIn this paper, spin‐to‐charge current conversion properties in the Weyl semimetal TaP by means of the inverse Rashba–Edelstein effect (IREE) with the interfacial integration of this quantum material with the ferromagnetic metal Permalloy (Py = Ni81Fe19) are presented. The spin currents are generated in the Py layer by the spin pumping effect (SPE) from microwave‐driven ferromagnetic resonance and are detected by a dc voltage along the TaP crystal, at room temperature. A field‐symmetric voltage signal is observed without the contamination of asymmetrical lines due to spin rectification effects observed in studies using metallic ferromagnets. The observed voltage is attributed to spin‐to‐charge current conversion based on the IREE, made possible by the spin–orbit coupling induced intrinsically by the bulk band structure of Weyl semimetals. The measured IREE coefficient λIREE = (0.30 ± 0.01) nm is two orders of magnitude larger than in graphene and is comparable to or larger than the values reported for some metallic interfaces and for several topological insulators.

Gate modulation of the spin current in graphene/WSe2 van der Waals heterostructure at room temperature

Two-dimensional transition metal dichalcogenide semiconductors owning a large intrinsic spin-orbit coupling (SOC) are considered the best candidates to generate, detect and manipulate the spin currents. The SOC defines the interconversion of spin and charge currents via Rashba Edelstein effect (spin Hall effect) and its reciprocal as inverse Rashba Edelstein effect (inverse spin Hall effect). However, the spin signal originated in low dimensional materials because of Rashba Edelstein effect or spin Hall effect yet needed to be addressed with distinguishable measurement technique. Here, we demonstrate experimentally the room temperature interconversion of spin and charge currents in Graphene/WSe 2 van der Waals heterostructure which is induced by proximity effect. Remarkably, the spin currents induced by Rashba Edelstein effect and spin Hall effect are discriminated and extracted individually via external magnetic field, respectively. The magnitude of spin transport and their corresponding spin efficiencies ( α RE E = 1.47 ± 0.03 % ) and (θ SHE = = 4.5 ± 0.07 % ) are modulated via applied electric field and temperature. Such electric, and magnetic field tunability of the spin transport through the non-magnetic materials may provide a new approach to fabricate the fast and low-power spintronic devices for quantum scale applications. • Experimental demonstration of interconversion of spin and charge currents in Graphene/WSe 2 van der Waals heterostructure, induced by proximity of WSe 2 , at room temperature. • Remarkably, the spin currents induced by Rashba Edelstein effect and spin Hall effect are discriminated and their corresponding spin efficiencies are extracted individually via external magnetic field, respectively.

Coherent Picture on the Pure Spin Transport between Ag/Bi and Ferromagnets.

In a joint effort of both experiments and first-principles calculations, we resolve a hotly debated controversy and provide a coherent picture on the pure spin transport between Ag/Bi and ferromagnets. We demonstrate a strong inverse Rashba-Edelstein effect (IREE) at the interface in between Ag/Bi with a ferromagnetic metal (FM) but not with a ferromagnetic insulator. This is in sharp contrast to the previously claimed IREE at Ag/Bi interface or inverse spin Hall effect dominated spin transport. A more than one order of magnitude modulation of IREE signal is realized for different Ag/Bi-FM interfaces, casting strong tunability and a new direction for searching efficient spintronics materials.

Interface-driven spin pumping and inverse Rashba-Edelstein effect in FeGaB/Ag/BiSb multilayers

Spin-orbit-coupling (SOC) plays a critical role in spin-to-charge conversion (SCC) mechanism. The SCC process is usually investigated by injecting a spin current from ferromagnet (FM) into a large SOC normal metal (SOC-NM) and then measuring the voltage generated by inverse spin Hall effect (ISHE). Recently, a new mechanism of SCC at inversion symmetry breaking interfaces between topological insulators (TIs) and magnetically ordered materials has been introduced, which is driven by the inverse Rashba-Edelstein effect (IREE). Motivated by this result, we have investigated the IREE effect of a simple binary three-dimensional TI Bi85Sb15 (BiSb). The model system used here is a trilayer of FeGaB/Ag/BiSb with different Ag thickness made insitu with a combination of dc magnetron sputtering and pulsed laser ablation. The SCC efficiency has been evaluated by measuring ferromagnetic resonance (FMR) driven ISHE voltage and extraction of the Gilbert damping (α) and interfacial spin mixing conductance (g↑↓) from the FMR line shape analysis. It is interesting to note that the charge current (Ic) increases with Ag thickness. This observation indicated that the IREE process at the Ag/BiSb interface dominates over ISHE in the bulk of BiSb film. The conversion efficiency of IREE is determined by calculating the IREE length (λIREE), which increases with the thickness of the Ag layer. These findings offer a method to generate and detect the IREE in a room temperature deposited heterostructure using simple coplanar waveguide setup.

Dissipationless Spin-Charge Conversion in Excitonic Pseudospin Superfluid.

Spin-charge conversion by the inverse spin Hall effect or inverse Rashba-Edelstein effect is prevalent in spintronics but dissipative. We propose a dissipationless spin-charge conversion mechanism by an excitonic pseudospin superfluid in an electron-hole double-layer system. Magnetic exchange fields lift singlet-triplet degeneracy of interlayer exciton levels in the double-layer system. Condensation of the singlet-triplet hybridized excitons breaks both a U(1) gauge symmetry and a pseudospin rotational symmetry around the fields, leading to spin-charge coupled superflow in the system. We demonstrate the mechanism by deriving spin-charge coupled Josephson equations for the excitonic superflow from a coupled quantum-dot model.

Terahertz emission from LaAlO<sub>3</sub>/SrTiO<sub>3</sub> heterostructures pumped with femtosecond laser

Since the discovery of the ultrafast demagnetization of the ferromagnetic metal, the spin degree of electrons is gradually used to generate terahertz radiation. The terahertz radiation generated by the inverse Rashba-Edelstein effect was confirmed first at the interface of Ag/Bi. However, the spin-to-charge conversion efficiency of the LaAlO<sub>3</sub>/SrTiO<sub>3</sub> interface is one order of magnitude lager than that of the Ag/Bi interface under equilibrium or quasi-equilibrium condition. Whether the LaAlO<sub>3</sub>/SrTiO<sub>3</sub> heterostructures can be used to convert spin current to generate terahertz radiation remains to be systemically studied. In this work, we fabricate the NiFe/LaAlO<sub>3</sub>//SrTiO<sub>3</sub> heterostructures and investigate the generation of terahertz radiation by femtosecond laser pumping and its dependence of the magnetic field direction. We change the thickness of the LaAlO<sub>3</sub> to show the applicability of the superdiffusive spin transport model and optical transmission model. We find the multireflections at the LaAlO<sub>3</sub>/SrTiO<sub>3</sub> interface weaken the terahertz radiation intensity. This work provides experimental and theoretical support for further optimizing the generation of terahertz electromagnetic waves.

Reliability of spin-to-charge conversion measurements in graphene-based lateral spin valves

Understanding spin physics in graphene is crucial for developing future two-dimensional spintronic devices. Recent studies show that efficient spin-to-charge conversions (SCCs) via either the inverse spin Hall effect or the inverse Rashba–Edelstein effect (IREE) can be achieved in graphene by proximity with an adjacent spin–orbit coupling (SOC) material. Lateral spin valve devices, made up of a graphene Hall bar and ferromagnets, are best suited for such studies. Here, we report that signals mimicking the IREE can be measured in pristine graphene possessing negligible SOC, confirming that these signals are unrelated to SCC. We identify either the anomalous Hall effect in the ferromagnet or the ordinary Hall effect in graphene induced by stray fields as the possible sources of this artefact. By quantitatively comparing these options with finite-element-method simulations, we conclude the latter better explains our results. Our study deepens the understanding of SCC measurement schemes in graphene, which should be taken into account when designing future experiments.

Growth optimization of TaN for superconducting spintronics

We have optimized the growth of superconducting TaN thin films on SiO2 substrates via dc magnetron sputtering and extract a maximum superconducting transition temperature of T c = 5 K as well as a maximum critical field μ 0 H c2 = (13.8 ± 0.1) T. This material is of interest for both different fields of quantum technology and superconducting spintronics as it represents a magnetic field-robust superconductor with strong spin–orbit interaction (SOI). After presenting the results of the growth optimization, we investigate in the second part the impact of the strong SOI in TaN on superconductor/ferromagnet heterostructures. To this end, we analyze the magnetization dynamics of both normal state and superconducting TaN/Ni80Fe20 (permalloy, Py)-bilayers as a function of temperature using broadband ferromagnetic resonance spectroscopy. In particular, we quantify the inverse current-induced torques of the bilayers and compare these results to NbN/Py-bilayers. In the normal state of TaN, we detect a positive damping-like current-induced torque σ d from the inverse spin Hall effect and a small field-like torque σ f attributed to the inverse Rashba–Edelstein effect at the TaN/Py-interface. In the superconducting state of TaN, we detect a negative σ d attributed to the quasiparticle mediated inverse spin Hall effect (QMiSHE) and the unexpected manifestation of a large positive field-like σ f of unknown origin matching our previous results for NbN/Py-bilayers. The QMiSHE can be used to probe spin currents in emergent quantum materials.

Giant inverse Rashba-Edelstein effect: Application to monolayer OsBi2

We propose that the hybridization between two sets of Rashba bands can lead to an unconventional topology where the two Fermi circles from different bands own in-plane helical spin textures with the same chiralities, and possess group velocities with the same directions. Under the weak spin injection, the two Fermi circles both give the positive contributions to the spin-to-charge conversion and thus induce the giant inverse Rashba-Edelstein Effect with large conversion efficiency, which is very different from the conventional Rashba-Edelstein Effect. More importantly, through the first-principles calculations, we predict that monolayer OsBi2 could be a good candidate to realize the giant inverse Rashba-Edelstein Effect. Our studies not only demonstrate a new mechanism to achieve highly efficient spin-to-charge conversion in spintronics, but also provide a promising material to realize it.

Unified Framework for Charge-Spin Interconversion in Spin-Orbit Materials

Materials with spin-orbit coupling are of great interest for various spintronics applications due to the efficient electrical generation and detection of spin-polarized electrons. Over the past decade, many materials have been studied, including topological insulators, transition metals, Kondo insulators, semimetals, semiconductors, and oxides; however, there is no unifying physical framework for understanding the physics and therefore designing a material system and devices with the desired properties. We present a model that binds together the experimental data observed on the wide variety of materials in a unified manner. We show that in a material with a given spin-momentum locking, the density of states plays a crucial role in determining the charge-spin interconversion efficiency, and a simple inverse relationship can be obtained. Remarkably, experimental data obtained over the last decade on many different materials closely follow such an inverse relationship. We further deduce two figure-of-merits of great current interest: the spin-orbit torque (SOT) efficiency (for the direct effect) and the inverse Rashba-Edelstein effect length (for the inverse effect), which statistically show good agreement with the existing experimental data on wide varieties of materials. Especially, we identify a scaling law for the SOT efficiency with respect to the carrier concentration in the sample, which agrees with existing data. Such an agreement is intriguing since our transport model includes only Fermi surface contributions and fundamentally different from the conventional views of the SOT efficiency that includes contributions from all the occupied states.

Negligible spin–charge conversion in Bi films and Bi/Ag(Cu) bilayers

Spin pumping experiments using ferromagnetic metals have reported highly efficient spin–charge conversion in Bi and at the Bi/Ag interface, possibly due to the inverse Rashba–Edelstein effect. However, longitudinal spin Seebeck effect experiments using the yttrium iron garnet ferrimagnetic insulator in Bi films and Bi/Ag bilayers do not show evidence of appreciable spin-to-charge conversion except the large Nernst signal inherent to Bi. These contrasting conclusions highlight the differences between magnetic metals and magnetic insulators as spin current injectors. Only the detected voltages that adhere to the inverse spin Hall effect of jC = (2e/ℏ)θSH jS × σ are due to spin currents.

Unveiling the spin-to-charge current conversion signal in the topological insulator Bi2Se3 by means of spin pumping experiments

We report an investigation of the spin-to-charge current conversion in sputter-deposited films of the topological insulator ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ onto single crystalline layers of yttrium iron garnet (YIG-${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$) and polycrystalline films of permalloy ($\mathrm{Py}\text{\ensuremath{-}}{\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$). Pure spin current was injected into the ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ layer by means of the spin pumping process produced by the spin precession in microwave driven ferromagnetic resonance of the ferromagnetic film. The spin-to-charge current conversion occurring at the ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$/ferromagnet interface is attributed to the inverse Rashba-Edelstein effect (IREE). From the data, we verified that the voltage generated by the spin-to-charge current conversion process in ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ has the same polarity as the inverse spin Hall effect in Ta, which is opposite to the one in Pt. Also, from the dependence of the voltage on the ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ thickness we were able the to calculate the IREE length values and found that $1.2\phantom{\rule{0.16em}{0ex}}\mathrm{pm}\ensuremath{\le}|{\ensuremath{\lambda}}_{\mathrm{IREE}}|\ensuremath{\le}2.2\phantom{\rule{0.16em}{0ex}}\mathrm{pm}$. This result allows us to conclude that indeed the surface states of ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ have a dominant role in the spin-to-charge current conversion process, and the mechanism based on the spin diffusion process plays a secondary role.

Enhanced Spin Seebeck Thermopower in Pt/Holey MoS2/Y3Fe5O12 Hybrid Structure.

We first observed the spin-to-charge conversion due to both the inverse Rashba-Edelstein effect (IREE) and inverse spin-Hall effect in a holey multilayer molybdenum disulfide (MoS2) intermediate layer in a Pt/YIG structure via LSSE measurements under nonequilibrium magnetization. We found an enhancement of approximately 238%, 307%, and 290% in the longitudinal spin Seebeck effect (LSSE) voltage, spin-to-charge current, and thermoelectric (TE) power factor, respectively, compared with the monolayer MoS2 interlayer in a Pt/YIG structure. Such an enhancement in the LSSE performance of Pt/holey MoS2/YIG can be explained by the improvement of spin accumulation in the Pt layer by induced spin fluctuation as well as increased additional spin-to-charge conversion due to in-plane IREE. Our findings represent a significant achievement in the understanding of spin transport in atomically thin MoS2 interlayers and pave the way toward large-area TE energy-harvesting devices in two-dimensional transition metal dichalcogenide materials.