arXiv subjects

Yandong Ma

Publications and source records attributed to Yandong Ma.

At least 19 recordsLinked to original sources

arXiv2026

Symmetry-Enforced Ferroelectric Switching of Two-Dimensional Altermagnetism

Altermagnetism features strong momentum-dependent spin splitting despite zero net magnetization, offering a transformative platform for next-generation spintronics. However, the nonvolatile and deterministic switching between its two equivalent spin-splitting states remains a fundamental bottleneck. Here, we propose a universal layer-engineering paradigm to achieve symmetry-enforced ferroelectric switching of two-dimensional altermagnetism. By sandwiching a conventional antiferromagnetic monolayer between two identical ferroelectric layers, the out-of-plane polarization cleanly breaks the spatial symmetry to induce robust altermagnetic splitting. Crucially, the global combined parity-time symmetry dictates that reversing the ferroelectric polarization exactly inverts the altermagnetic spin-splitting pattern. We rigorously validate this mechanism in the In2Se3/MnPTe3/In2Se3 trilayer using first-principles calculations. As a direct consequence, the ferroelectrically driven spin-splitting reversal deterministically flips the anomalous Hall effect signal, providing an unambiguous transport fingerprint to electrically distinguish the two altermagnetic states. Unconstrained by the stringent symmetry requirements of intrinsic single-phase materials, our findings establish a versatile physical framework for electrically addressable altermagnetic spintronics.

cond-mat.mtrl-sci↗

arXiv2026

Symmetry-dictated switching of antiferromagnetic magnon transport in 2D multiferroics

While antiferromagnetic magnons in two-dimensional (2D) materials hold immense promise for high-frequency spintronics, achieving their efficient active control remains a critical challenge. Here, we propose a universal mechanism for the nonvolatile ferroelectric (FE) switching of antiferromagnetic magnon transport in 2D multiferroic lattices. Our mechanism relies on coupling the magnon geometric phase to the FE-induced sublattice asymmetry in exchange and Dzyaloshinskii-Moriya interactions. This explicitly breaks the exact compensation of opposite-chirality magnons inherent to collinear antiferromagnets, lifting their spin degeneracy and inducing a highly tunable net Berry curvature. Crucially, reversing the FE polarization deterministically swaps these magnetic asymmetries, which completely inverts the net magnon Berry curvature and the resulting anomalous thermal Hall conductivity. Using first-principles and linear spin-wave theory, we rigorously validate this geometric-phase-driven mechanism in single-layer CuCr2Se4. Our findings establish a robust paradigm for coupling multiferroicity with the magnon geometric phase, paving the way for nonvolatile and electrically switchable antiferromagnetic magnonics.

cond-mat.mtrl-sci↗

arXiv2026

Symmetry-Driven Electrical Switching of Anisotropic Skyrmion Hall Effect in Altermagnets

Controlling the skyrmion Hall effect (SkHE) is pivotal for developing topological spintronics but typically relies on magnetic field reversal. Here, we demonstrate a general strategy for the purely electrical switching of the SkHE in two-dimensional altermagnets. Through symmetry and model analysis, we reveal that the intrinsic altermagnetic symmetry imposes sublattice-dependent anisotropic exchange and Dzyaloshinskii-Moriya interactions. These interactions induce a highly anisotropic SkHE, where the transverse velocity is strictly dictated by the current direction relative to the crystal axes. Crucially, we show that an external electric field can strongly modulate these interaction parameters by inversing the altermagnetic symmetry, allowing for the reversible inversion of the anisotropic SkHE. Using first-principles and atomistic spin model simulations, this mechanism is further demonstrated in monolayer CaMnSn. Our study establishes a unique strategy for realizing precise, electrically tunable skyrmion transport without magnetic fields.

cond-mat.mtrl-sci↗

arXiv2026

Moire Topological Magnetism Twist-Engineered from 2D Spin Spirals

Topological magnetism, characterized by topologically protected spin textures, offers rich physics and transformative prospects for spintronics. However, its stabilization typically demands external magnetic fields, preventing straightforward implementation. Here, we report a universal field-free approach for engineering 2D topologically-trivial spin spirals into topological magnetisms. This approach leverages twisted antiferromagnetic bilayers, where locked spin spirals in the two sublayers form spatially alternating ferromagnetic and antiferromagnetic domains upon twisting. These domains frustrate the uniform antiferromagnetic interlayer exchange, spontaneously stabilizing moire topological magnetisms without external fields. Using first-principles and atomistic spin-model simulations, we validate this approach using bilayers NiCl2 and NiBr2, as representative examples. For twisted NiCl2, we predict topological spin states tunable by the twist angle, including isolated and high-order antiferromagnetic bimerons. For twisted NiBr2, strong frustration yields trivial triple-q spin spirals, which transform into moire topological magnetism with the application of vertical compressive strain. Our findings demonstrate that topologically non-trivial spin textures can be engineered from their trivial counterparts, thus providing a new paradigm for topological spintronics

cond-mat.mtrl-sci↗

arXiv2026

Design of Skyrmion Bags with Tunable Topology in Symmetry-Broken 2D Lattices

Magnetic skyrmion bags, as high-order topological swirling spin textures, offer rich fundamental physics and distinct advantages for spintronic applications; however, their realization remains a formidable challenge, especially in two-dimensional (2D) systems. Here, through model analysis, we propose a novel design principle for engineering skyrmion bags with tunable topology in symmetry-broken 2D ferromagnetic lattices. The physics correlates to the delicate interplay of isotropic exchange interaction, Dzyaloshinskii-Moriya interaction and magnetic anisotropy, which can stabilize a rich variety of high-order topological spin states as well as the intriguing skyrmionium with zero topological charge. We further validate this mechanism in monolayer CrInTe2 using first-principles calculations and atomistic spin model simulations, revealing the existence of field-free skyrmion bags. Furthermore, we find that a weak magnetic field triggers a transition to skyrmioniums that exhibit remarkable thermal stability up to 240 K. Our results provide a compelling platform for exploring high-order topological magnetism.

cond-mat.mtrl-sci↗

arXiv2026

Altermagnetic Skyrmions in 2D Lattices Exhibiting Anisotropic Skyrmion Hall Effect

Anisotropic skyrmion Hall effect (A-SkHE) in two-dimensional (2D) magnetic systems represents a captivating phenomenon in condensed-matter physics and materials science. While conventional antiferromagnetic systems inherently suppress this effect through parity-time symmetry-mediated cancellation of Magnus forces acting on skyrmions, A-SkHE is primarily confined to ferromagnetic platforms. Here, we present a paradigm-shifting demonstration of this phenomenon in spin-splitting 2D antiferromagnets through the investigation of altermagnetic skyrmions. Combining comprehensive symmetry analysis with theoretical modeling, we elucidate the mechanism governing A-SkHE realization in 2D altermagnetic systems and establish a quantitative relationship between the transverse velocity of altermagnetic skyrmions and applied current orientation. Using first-principles calculations and micromagnetic simulations, this mechanism is further illustrated in a prototypical altermagnetic monolayer V2SeTeO. Crucially, we identify that the [C2C4zt] symmetry-protected anisotropic field serves as the critical stabilizer for maintaining the A-SkHE in this system. Our results greatly enrich the research on 2D altermagnetism and skyrmions.

cond-mat.mtrl-sci↗

arXiv2026

Ordering Mixed-Q Topological Magnetism into Lattice via Moire Engineering

Topological magnetic lattices offer a fertile ground for exploring fundamental physics and developing novel spintronic devices. However, current research is predominantly confined to single-Q topologies hosting uniform type of quasiparticle. The realization of exotic mixed-Q states, where distinct topological quasiparticles co-assemble into an ordered lattice, remains largely unexplored. Here, we propose a generic mechanism to order disordered mixed-Q topological magnetism into periodic lattice via moire engineering. By leveraging the synergy between spatially modulated interlayer coupling and intrinsic intralayer magnetic frustration, we demonstrate that moire potential can effectively regularize skyrmions, antiskyrmions, and magnetic bubbles into a hybrid lattice. Combining first-principles with atomistic spin simulations, we validate this mechanism in twisted bilayer CrGaTe3, identifying it as an exemplary platform for hosting these complex ordered textures. We systematically map the phase evolution as a function of twist angle and biaxial strain, unveiling the critical role of moire potential in stabilizing mixed-Q lattice. Our findings significantly advance the frontier of topological and moire spintronics.

cond-mat.mtrl-sci↗

arXiv2025

Engineering Spin Splitting in Antiferromagnets by Superatoms with Internal Degree of Freedom

Superatoms, stable atomic clusters acting as building blocks for new materials, offer unique opportunities due to their rich properties and potential for 2D material assembly. While extensive research has focused on their similarities to ordinary atoms, the role of their internal degrees of freedom (IDOF) remains largely unexplored. Concurrently, compensated antiferromagnets (AFMs) with intrinsic spin-split band structures have emerged as a promising class of materials for spintronics, yet their experimental realization, particularly in two dimensions, is limited. Here, we bridge these two fields by proposing a novel strategy to achieve spin-split AFMs using superatoms with IDOFs. We establish our core concept using a simple model, demonstrating how superatom IDOFs can be leveraged to engineer system symmetry and induce spin splitting in AFM states. We concretely illustrate this strategy by first-principles calculations on a Mo-decorated carborophene sheets, constructed from closo-carborane superatoms. We show that the distinct IDOFs of carborane isomers (electric-dipole-like and nematic) are critical in determining the symmetry of the resulting 2D superatomic crystal and, consequently, the spin splitting pattern of its AFM states. Our findings underscore the profound significance of superatom IDOFs-a feature absent in ordinary atoms-and introduce a new paradigm for engineering spin splitting in AFM lattices. This work opens novel avenues for the design of advanced spintronic and quantum materials based on superatoms.

cond-mat.mtrl-sci↗

arXiv2025

Light-Induced Spin Slanting in 2D Multiferroic Magnet

Controlling spin orientation of two-dimensional (2D) materials has emerged as a frontier of condensed-matter physics, resulting in the discovery of various phases of matter. However, in most cases, spin orientation can be stablished only at specific directions of out-of-plane and in-plane, which is a drawback compared with three-dimensional systems, limiting exploration of novel physics. Here, we introduce a methodology for manipulating spin slanting in 2D multiferroic materials through ultrafast pulses of light. Based on model analysis, we find that simultaneous triggering spin-orbit coupling induced interactions from in-plane and out-of-plane orbitals can generate spin slanting. By choosing 2D multiferroic materials with specific low-energy composition endowed by symmetry, such triggering can be readily achieved through ultrafast light illumination, leading to light-induced spin slanting. Using real-time time-dependent density-functional theory, we demonstrate this approach in multiferroic single-layer CuCr2Se4. This study provides an efficient way to manipulate spin orientation in 2D materials and establishes a general platform to explore physics and applications associated with spin slanting.

cond-mat.mes-hall↗

arXiv2024

Ultrafast laser driven ferromagnetic-antiferromagnetic skyrmion switching in 2D topological magnet

Light-spin coupling is an attractive phenomenon from the standpoints of fundamental physics and device applications, and has spurred rapid development recently. Whereas the current efforts are devoted to trivial magnetism, the interplay between light and nontrivial spin properties of topological magnetism is little known. Here, using first principles, rt-TDDFT and atomic spin simulations, we explore the evaluation of topological spin properties of monolayer CrInSe3 under laser, establishing the ultrafast ferromagnetic-antiferromagnetic skyrmion reversal. The physics correlates to the laser-induced significant spin-selective charge transfer, demagnetization, and time-dependent magnetic interactions. Especially, an essential switching from ferromagnetic to antiferromagnetic exchange is generated under light irradiation. More importantly, dynamics of topological magnetic physics shows that this process accompanies with the evaluation of topological magnetism from ferromagnetic to antiferromagnetic skyrmions, manifesting intriguing interplay between light and topological spin properties. Our letter provides a novel approach toward the highly desired ultrafast control of topological magnetism.

cond-mat.mtrl-sci↗

arXiv2024

Gate-Controllable Quadri-Layertronics in 2D Multiferroic Antiferromagnet

Layertronics that manifests layer Hall effect is typically considered to intrinsically possess binary physics. Using symmetry arguments and a low-energy kp model, we show that the layer physics in layertronics can be engineered into quaternary mode, giving rise to the concept of quadri-layertronics. The mechanism correlates to the interplay between out-of-plane ferroelectricity and valley physics in antiferromagnetic multiferroic quadrilayer, which enables the layer-locked Berry curvature and Hall effect, i.e., deflecting the carriers with four different layer physics to move in specific directions. More importantly, the quadri-layertronics can be generated and manipulated by controlling the interlayer dipole arrangements via a gate voltage, allowing for the selective induction and detection of layer Hall effect in specific layers. Using first principles calculations, we further demonstrate the gate control of quadri-layertronics in multiferroic antiferromagnet of quadrilayer OsCl2. These explored phenomena and insights greatly enrich the research on layertronics.

cond-mat.mtrl-sci↗

arXiv2024

Ferro-Valleytricity with In-Plane Magnetization

Ferro-valleytricity, a fundamental phenomenon that manifests spontaneous valley polarization, is generally considered to occur in two-dimensional (2D) materials with out-of-plane magnetization. Here, we propose a mechanism to realize ferro-valleytricity in 2D materials with in-plane magnetization, wherein the physics correlates to non-collinear magnetism in triangular lattice. Our model analysis provides comprehensive ingredients that allows for in-plane ferro-valleytricity, revealing that mirror symmetry is required for remarkable valley polarization and time-reversal-mirror joint-symmetry should be excluded. Through modulating in-plane magnetization offset, the valley polarization could be reversed. Followed by first-principles, such mechanism is demonstrated in a multiferroic triangular lattice of single-layer W3Cl8. We further show that the reversal of valley polarization could also be driven by applying electric field that modulates ferroelectricity. Our findings greatly enrich the valley physics research and significantly extend the scope for material classes of ferro-valleytricity.

cond-mat.mtrl-sci↗

arXiv2024

Coupling multi-space topologies in 2D ferromagnetic lattice

Topology can manifest topological magnetism (e.g., skyrmion and bimeron) in real space and quantum anomalous Hall (QAH) state in momentum space, which have changed the modern conceptions of matter phase. While the topologies in different spaces are widely studied separately, their coexistence and coupling in single phase is seldomly explored. Here, we report a novel phenomenon that arises from the interaction of topological magnetism and band topology, the multi-space topology, in 2D ferromagnetic lattice. Based on continuum theory and tight-binding model, we reveal that the interconnection between skyrmion/bimeron and QAH state generates distinctive localized chiral bound states (CBSs). With moderating topological magnetism through magnetic field, the multi-space topologies accompanied with different CBSs can be reversed, facilitating the coupling of multi-space topologies. By performing firstprinciples and atomic spin model simulations, we further demonstrate such multi-space topologies and their coupling in monolayer Cr2NSb. These results represent an important step towards the development of multispace topological phenomena in 2D lattice.

cond-mat.mtrl-sci↗

arXiv2024

Ferroelectrovalley in Two-Dimensional Multiferroic Lattices

Engineering valley index is essential and highly sought for valley physics, but currently it is exclusively based on the paradigm of the challenging ferrovalley with spin-orientation reversal under magnetic field. Here, an alternative strategy, i.e., the so-called ferroelectrovalley, is proposed to tackle the insurmountable spin-orientation reversal, which reveres valley index with the feasible ferroelectricity. Using symmetry arguments and tight-binding model, the C_2 rotation is unveiled to be able to take the place of time reversal for operating valley index in two-dimensional multiferroic kagome lattices, which enables the ferroelectricity-engineered valley index, thereby generating the concept of ferroelectrovalley. Based on first-principles calculations, this concept is further demonstrated in the breathing kagome lattice of single-layer Ti3Br8, wherein ferroelectricity couples the breathing process. These findings open a new direction for valleytronics and two-dimensional materials research.

cond-mat.mtrl-sci↗

arXiv2023

Bloch-type magnetic skyrmions in two-dimensional lattice

Magnetic skyrmions in two-dimensional lattice are a prominent topic of condensed matter physics and material science. Current research efforts in this field are exclusively constrained to Neel-type and antiskyrmion, while Bloch-type magnetic skyrmions are rarely explored. Here, we report the discovery of Bloch-type magnetic skyrmions in two-dimensional lattice of MnInP2Te6, using firstprinciples calculations and Monte-Carlo simulations. Arising from the joint effect of broken inversion symmetry and strong spin-orbit coupling, monolayer MnInP2Te6 presents large Dzyaloshinskii-Moriya interaction. This, along with ferromagnetic exchange interaction and out-ofplane magnetic anisotropy, gives rise to skyrmion physics in monolayer MnInP2Te6, without needing magnetic field. Remarkably, different from all previous works on two-dimensional lattice,the resultant magnetic skyrmions feature Bloch-type, which is protected by D3 symmetry.Furthermore, the Bloch-type magnetic bimerons are also identified in monolayer MnTlP2Te6. The phase diagrams of these Bloch-type topological magnetisms under magnetic field, temperature and strain are mapped out. Our results greatly enrich the research on magnetic skyrmions in twodimensional lattice.

cond-mat.mtrl-sci↗

arXiv2022

Multiple Topological Magnetism in van der Waals Heterostructure of MnTe2/ZrS2

Topological magnetism in low-dimensional systems is of fundamental and practical importance in condensed-matter physics and material science. Here, using first-principles and Monte-Carlo simulations, we present that multiple topological magnetism (i.e., skyrmion and bimeron) can survive in van der Waals Heterostructure of MnTe2ZrS2. Arising from interlayer coupling, MnTe2ZrS2 can harbor a large Dzyaloshinskii-Moriya interaction. This, combined with ferromagnetic exchange interaction, yields an intriguing skyrmion phase consisting of sub-10 nm magnetic skyrmions under a tiny magnetic field of 75 mT. Meanwhile, upon harnessing a small electric field, magnetic bimeron can be observed in MnTe2ZrS2 as well, suggesting the existence of multiple topological magnetism. Through interlayer sliding, both topological spin textures can be switched on-off, suggesting their stacking-dependent character. In addition, the impacts of d and Keff on these spin textures are revealed, and a dimensionless parameter is utilized to describe their joint effect. These explored phenomena and insights not only are useful for fundamental research in topological magnetism, but also enable novel applications in nanodevices.

cond-mat.mtrl-sci↗

arXiv2022

Intrinsic Layer-Polarized Anomalous Hall Effect in Bilayer MnBi2Te4

Layer-polarized anomalous Hall effect (LP-AHE) is an attractive phenomenon in condensed-matter physics from the standpoints of both fundamental interest and device applications. The current LP-AHE research is based on the extrinsic paradigm of using external electric fields, in which the generation and control of LP-AHE are not straightforward. Here, we propose a novel mechanism that realizes intrinsic LP-AHE in bilayer lattices, through the mediation of sliding physics and Berry curvature. Moreover, this mechanism could render the LP-AHE in a controllable and reversable fashion. We analyze the symmetry requirements for a system to host such intrinsic LP-AHE. Its validity is further demonstrated in a real material of bilayer MnBi2Te4. By stacking with broken inversion symmetry, the layer-locked Berry curvature enables the intrinsic LP-AHE in bilayer MnBi2Te4, and the switchable control of its LP-AHE is achieved by sliding ferroelectricity. Our work opens a significant new direction for LP-AHE and two-dimensional (2D) materials research.

cond-mat.mtrl-sci↗

arXiv2022

Layer-Polarized Anomalous Hall Effect in Valleytronic van der Waals Bilayers

Layer-polarized anomalous Hall effect (LP-AHE), derived from the coupling between Berry curvature and layer degree of freedom, is of importance for both fundamental physics and device applications. Nonetheless, the current research paradigm is rooted in topological systems, rendering such phenomenon rather scarce. Here, through model analysis, we propose an alternative, but general mechanism to realize the LP-AHE in valleytronic van der Waals bilayers by interlayer sliding. The interaction between the out-of-plane ferroelectricity and A-type antiferromagnetism gives rise to the layer-locked Berry curvature and thus the long-sought LP-AHE in the bilayer systems. The LP-AHE can be strongly coupled with sliding ferroelectricity, to enable ferroelectrically controllable and reversible. The mechanism is demonstrated in a series of real valleytronic materials, including bilayer VSi2P4, VSi2N4, FeCl2, RuBr2 and VClBr. The new mechanism and phenomena provide a significant new direction to realize LP-AHE and explore its application in electronics.

cond-mat.mtrl-sci↗