arXiv subjects

Dahai Wei

Publications and source records attributed to Dahai Wei.

8 recordsLinked to original sources

arXiv2026

Evidence of Crystal-Field-Mediated Anisotropic Orbital Rashba Effect in Epitaxial Ru/FM Heterostructure

Electrical generation of orbital angular momentum provides a promising route to current-induced torques, yet effective control of orbital Rashba textures still remains challenging, particularly because the role of the interfacial crystal field remains largely unexplored. Here, we report experimental evidence for a crystal-field-mediated interfacial anisotropic orbital Rashba effect (AORE) in epitaxial Ru/ferromagnet heterostructures. Total orbital torque was disentangled into an isotropic bulk contribution and an in-plane anisotropic interfacial contribution. The latter was strongly suppressed by degrading the crystallinity of either constituent and by inserting a Cu spacer, highlighting the essential roles of coherent interfacial orbital hybridization and direct Ru/ferromagnet contact. These results identify interfacial crystal-field coherency as a key ingredient in manipulating orbital Rashba textures and establish a route toward engineering the symmetry and directionality of orbital torques.

cond-mat.mes-hall↗

arXiv2026

Effects of Impurity Scattering on Orbital Hall Conductivity and Orbital Transport in Ru-based Alloys

The role of impurity scattering in the generation and transport of orbital current remains less established than in conventional spin Hall systems. Here we investigate Ru-based nonmagnet/ferromagnet bilayers in which the impurity scattering is tuned by Cu or Ti alloying. According to SOT measurement and thickness-dependent drift-diffusion analysis, we extract the effective orbital Hall conductivity and the orbital diffusion length. We find that the orbital Hall effect in polycrystalline Ru is dominated by intrinsic mechanism that is moderately robust against weak disorder but suppressed by stronger alloy disorder. However, the orbital diffusion length remains nearly unchanged at approximately 14 nm over the investigated impurity range. This behavior indicates that orbital transport is not governed simply by an impurity scattering. Together with previous temperature-dependent measurements, our results show that static impurities and dynamic lattice disorder affect orbital transport through distinct microscopic channels. These results provide new insight into how disorder governs orbital generation and transport, and offer experimental guidance for developing high-efficient orbitronic materials.

cond-mat.mes-hall↗

arXiv2026

Absence of Orbital Hall Magnetoresistance in Nonmagnet/Ferromagnet Bilayers with Large Orbital Torque

We report the absence of orbital Hall magnetoresistance (OMR) in nonmagnet/ferromagnet bilayers, challenging the general assumption that orbital transport mimics spin transport. Despite the observation of giant orbital torques, confirming the generation of orbital currents, thickness-dependent magnetoresistance measurements reveal that the signal is dominated by the intrinsic magnetoresistance of the ferromagnet and current shunting, with no discernible OMR contribution. We attribute this contradiction to the distinct transport properties of orbital compared with spin. Orbital currents undergo isotropic bulk absorption in the ferromagnet rather than anisotropic interfacial reflection required for OMR. Furthermore, we find that texture-induced magnetoresistance and self-torques in Ni-based bilayers can generate misleading signals, suggesting that caution is required when employing Ni in orbitronic studies. These findings clarify the distinct physical rules governing orbital transport and provide a simple method to distinguish spin and orbital currents.

cond-mat.mes-hall↗

arXiv2025

Chiral dual spin currents field-free perpendicular switching by altermagnet RuO2

Conventional spintronic mechanisms, such as spin-transfer and spin-orbit torques based on the spin current, rely on breaking time-reversal symmetry to manipulate magnetic moments. In contrast, for spatially separated dual spin currents, the time-reversal-invariant vector chirality emerges as a critical factor governing magnetization dynamics. Here, we investigate field-free perpendicular magnetization switching in an altermagnet RuO2/ferromagnet/heavy metal Pt trilayer, driven by chiral dual spin currents (CDSC). We demonstrate that the chirality of these dual spin currents acts as the deterministic role in breaking out-of-plane symmetry. Leveraging the intrinsic spin-splitting effect of the d-wave altermagnet to generate an x-polarized spin component, the interplay of non-collinear spin currents from two adjacent layers induces a helical magnetic texture within the intermediate layer. The resulting intralayer exchange coupling manifests as an effective in-plane magnetic field, facilitating deterministic switching. This distinct physical picture, validated by switching measurements and micromagnetic simulations, reveals that the switching polarity is dictated by chirality rather than charge current polarity. Characterized by the novel symmetry and low power consumption, CDSC offers a promising paradigm for next-generation high-performance spintronic architectures.

cond-mat.mes-hall↗

arXiv2021

Room temperature energy-efficient spin-orbit torque switching in wafer-scale all-vdW heterostructure

The emergent two-dimensional (2D) ferromagnetic materials with unique magnetic properties have endowed great potential for next-generation spintronic devices with extraordinary merits of high flexibility, easy controllability, and high heretointegrability, which is expected to promote the development of Moore's Law continuously. However, it is extremely challenging to realize magnetic switching with ultra-low power consumption at room temperature. Here, we demonstrate the room-temperature spin-orbit torque (SOT) driven magnetization switching in a well-epitaxial all-van der Waals (vdW) heterostructure. The topological insulator Bi2Te3 not only helps to elevate the Curie temperature of Fe3GeTe2 (FGT) through interfacial exchange coupling but also works as a spin current source allowing to switch FGT at a low current density of 2.2 * 106 A cm2. A large SOT efficiency of 0.7 is measured at room temperature, and the thickness of FGT is further adjusted to reduce the influence of the thermal contribution on the second-harmonic signal. Furthermore, the temperature and thickness-dependent SOT efficiency prove that the large SOT in our system mainly originates from the nontrivial origin of topological materials. Our experiment has enabled an all-vdW SOT structure and lays a solid foundation for the implementation of room-temperature all-vdW spintronic devices in the future.

physics.app-ph↗

arXiv2013

Experimental observation of a large ac-spin Hall effect

In spinelectronics the spin degree of freedom is used to transmit and store information. Ideally this occurs without net charge currents in order to avoid energy dissipation due to Joule heating. To this end the ability to create pure spin currents i.e.without net charge transfer is essential. Spin pumping is the most popular approach to generate pure spin currents in metals, semiconductors, graphene, and even organic materials. When the magnetization vector in a ferromagnet (FM) - normal metal (NM) junction is excited the spin pumping effect leads to the injection of pure spin currents in the normal metal. The polarization of this spin current is time dependent and contains a very small dc component. The dc-component of the injected spin current has been intensely studied in recent years and has given rise to controversial discussions concerning the magnitude the spin Hall angle which is a material dependent measure of the efficiency of spin to charge conversion . However in contrast to the rather well understood dc component the two orders of magnitude larger ac component has escaped experimental detection so far. Here we show that the large ac component of the spin currents can be detected very efficiently using the inverse spin Hall effect (ISHE). The observed ac-ISHE voltages are one order of magnitude larger than the conventional dc-ISHE measured on the same device. The spectral shape, angular dependence, power scaling behavior and absolute magnitude of the signals are in line with spin pumping and ISHE effects. Our results demonstrate that FM-NM junctions are very efficient sources of pure spin currents in the GHz frequency range and we believe that our result will stimulate the emerging field of ac spintronics.

cond-mat.mes-hall↗

arXiv2013

Experimental Verification of Comparability between Spin-Orbit and Spin-Diffusion Lengths

We experimentally confirmed that the spin-orbit lengths of noble metals obtained from weak anti-localization measurements are comparable to the spin diffusion lengths determined from lateral spin valve ones. Even for metals with strong spin-orbit interactions such as Pt, we verified that the two methods gave comparable values which were much larger than those obtained from recent spin torque ferromagnetic resonance measurements. To give a further evidence for the comparability between the two length scales, we measured the disorder dependence of the spin-orbit length of copper by changing the thickness of the wire. The obtained spin-orbit length nicely follows a linear law as a function of the diffusion coefficient, clearly indicating that the Elliott-Yafet mechanism is dominant as in the case of the spin diffusion length.

cond-mat.mes-hall↗

arXiv2012

Bi(111) thin film with insulating interior but metallic surfaces

The electrical conductance of molecular beam epitaxial Bi on BaF2(111) was measured as a function of both film thickness (4-540 nm) and temperature (5-300 K). Unlike bulk Bi as a prototype semimetal, the Bi thin films up to 90 nm are found to be insulating in the interiors but metallic on the surfaces. This result has not only resolved unambiguously the long controversy about the existence of semimetal-semiconductor transition in Bi thin film but also provided a straightforward interpretation for the long-puzzled temperature dependence of the resistivity of Bi thin films, which in turn might suggest some potential applications in spintronics.

cond-mat.mes-hall↗