Ying Dai

Antiferromagnetic spintronics promises ultrafast device performance, yet the essential Néel vector reversal is hindered by its intrinsic immunity to external magnetic fields. Here, we propose a mechanism for deterministic Néel vector reversal in 2D van der Waals antiferromagnets enabled by ultrafast laser pulses. The core physics involves light-induced asymmetric interlayer demagnetization, which drives the antiferromagnet into a transient ferrimagnetic state with a finite net moment. This transient symmetry breaking allows the Néel vector to be controlled by an external magnetic field. We identify that the intrinsic structural and electronic asymmetries and spin–orbit-coupling mediated spin flips are essential for this process. Using first-principles calculations and real-time time-dependent density functional theory, we further demonstrate this mechanism in bilayer NiICl and YI2. Our work establishes a general strategy for the optical manipulation of 2D antiferromagnetic order.

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. Here, Q denotes the real-space topological charge of a spin texture, rather than a reciprocal-space ordering wavevector. The realization of exotic mixed-Q states, where distinct topological quasiparticles coassemble into an ordered lattice, remains largely unexplored. Here, we propose a design principle to order disordered mixed-Q topological magnetism into periodic lattice via moiré engineering. By leveraging the synergy between spatially modulated interlayer coupling and intrinsic intralayer magnetic frustration, we demonstrate that moiré 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 moiré potential in stabilizing mixed-Q lattice. Our findings significantly advance the frontier of topological and moiré spintronics.

Deterministic switching of skyrmion topology is a central frontier in topological spintronics, yet current paradigms rely almost exclusively on dissipative-current-driven spin torques. Here, we propose a fundamentally distinct mechanism for the nonvolatile switching of the skyrmion topology in two-dimensional multiferroics. We reveal that the intrinsic magnetoelectric coupling intimately links the out-of-plane ferroelectric polarization to interlayer magnetic exchange. Consequently, an electric-field-driven polarization reversal deterministically converts the interlayer coupling between the ferromagnetic and antiferromagnetic states. This macroscopic exchange reversal directly flips the microscopic skyrmion core polarity and reverses its topological charge, thereby stabilizing the two electrically addressable topological phases. Guided by our established design principles, we rigorously validate this mechanism in a Co2CF2/MoN2 multiferroic heterostructure by using combined first-principles calculations and atomistic spin simulations. Our findings bypass the limitations of continuous current injection, establishing a robust physical framework for energy-efficient multiferroic topological spintronics.

The electrochemical CO2 reduction reaction (CO2RR) on Cu surfaces is constrained by the scaling relations among intermediate adsorption energies. We demonstrate that Cu-terminated Ti3CuC2, featuring an atomically thin Cu monolayer, is an efficient CO2RR catalyst. Charge transfer from Ti3C2 to Cu enriches the reaction sites with electrons and thus reconstructs their local electronic environment, downshifting the Cu d-band center. This regulation selectively enhances CO2 adsorption while it attenuates CO binding. The potential-determining step is hence diverted from *CO + H+ + e– → *CHO to alternative steps (ΔG = 0.02 eV). Such a mechanistic shift leads to low limiting potentials of −0.20 V for CH3OH and −0.30 V for CH4, simultaneously transforming the formidable C–C coupling into an exothermic process (ΔG = −0.10 eV) and enabling favorable pathways toward C2H4 and C2H5OH. These findings establish the selective regulation of CO2/CO adsorption as a promising design principle for efficient CO2RR catalysts.

Ferroelectric switching in van der Waals heterostructures provides a powerful route to reconfiguring quantum states and their associated transport responses. Here, we propose a ferroelectric topological heterobilayer in which the stepwise reversal of polarization in the two monolayers enables selective control of spin and orbital transport with reduced mutual interference. Using first-principles calculations, we identify the In2Te3/In2Se3 heterobilayer as a candidate, where this stepwise polarization switching drives successive topological phase transitions from second-order topological to quantum spin Hall insulators and eventually to a trivial metal. These three phases exhibit distinct transport characteristics, including pure orbital Hall effect (OHE), layer-resolved coexistence of spin Hall effect (SHE) and OHE, and a metallic state with simultaneously enhanced SHE and OHE, accompanied by pronounced changes in the layer distribution of carriers. Our work highlights ferroelectric topological heterobilayers as a promising platform for controlling and characterizing spin–orbitronic transport, with potential for integrated spintronic and orbitronic devices.

Altermagnetic multiferroicity is rapidly emerging as a transformative paradigm for both condensed matter physics and advanced spintronics. However, existing magnetoelectric mechanisms are inherently restricted to structural inversions, which merely reverse the momentum‐space spin splitting. Here, guided by symmetry principles and microscopic modeling, we unveil an emergent class of altermagnetic multiferroicity in 2D heterobilayers. This mechanism utilizes out‐of‐plane ferroelectric polarization to govern the interlayer coupling, thereby tuning the competition between localized antiferromagnetic superexchange and itinerant ferromagnetic double‐exchange. Crucially, this interfacial modulation triggers a reversible magnetic phase transition between a trivial ferromagnetic state and an altermagnetic state, establishing a distinct magnetoelectric coupling mechanism. Using first‐principles calculations, we demonstrate this mechanism in MnPS ₃ /Sc ₂ CO ₂ heterostructure, where we further predict the emergence of two distinct altermagnetic phases. Our findings transcend geometric restrictions, establishing a physical framework for nonvolatile and programmable altermagnetic spintronics.

Altermagnetism is a newly identified magnetic phase, constituting a third class of magnets with momentum-dependent spin splitting but vanishing net magnetic moment. Here, unlike the widely considered circularly polarized light that yields a normal insulating phase, we put forward that Floquet engineering under elliptically polarized light induces Floquet quantum anomalous Hall (QAH) effect in two-dimensional (2D) altermagnets with out-of-plane magnetization. Notably, Floquet–Bloch band engineering enables switchable chirality via manipulating the intensity and/or polar angle. Furthermore, we identify the Fe2Te2O monolayer as a realistic candidate hosting nontrivial phenomena, where topological phase transitions from a topological crystalline insulator (TCI) to a QAH insulator and between QAH insulators with opposite chirality emerge, as confirmed by first-principles calculations. These findings establish the feasibility of realizing the QAH effect in 2D altermagnets and provide an experimentally accessible avenue toward next-generation high-speed, optically controlled topological electronic devices.

Altermagnetism has recently emerged as a promising platform for achieving exotic quantum states and dissipationless spin transport. Here, we uncover a previously unexplored Floquet realization of the quantum spin Hall effect in 2D altermagnets under elliptically polarized light, a phenomenon that has remained unattainable in previously studied ferromagnetic and antiferromagnetic systems. Remarkably, accompanying the periodic driving, the system undergoes successive topological phase transitions from a second-order topological insulator to a quantum anomalous Hall insulator, and ultimately to a quantum spin Hall insulator. Moreover, the proposed mechanism is confirmed in the altermagnetic V2SSeO monolayer through analyses of corner states, edge states, and quantized anomalous and spin Hall responses, establishing it as a realistic material platform. Our findings establish a link between altermagnetism, Floquet engineering, and topological phases, opening new possibilities for next-generation optically controlled topological spintronic devices.

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.