Engineering Layertronics in Two-Dimensional Ferromagnetic Multiferroic Lattice.

Layertronics, rooted in the layer Hall effect (LHE), is an emerging fundamental phenomenon in condensed matter physics and spintronics. So far, several theoretical and experimental proposals have been made to realize LHE, but all are based on antiferromagnetic systems. Here, using symmetry and tight-binding model analysis, we propose a general mechanism for engineering layertronics in a two-dimensional ferromagnetic multiferroic lattice. The physics is related to the band geometric properties and multiferroicity, which results in the coupling between Berry curvature and layer degree of freedom, thereby generating the LHE. Using first-principles calculations, we further demonstrate this mechanism in bilayer (BL) TcIrGe2S6. Due to the intrinsic inversion and time-reversal symmetry breakings, BL TcIrGe2S6 exhibits multiferroicity with large Berry curvatures at both the center and corners of the Brillouin zone. These Berry curvatures couple with the layer physics, forming the LHE in BL TcIrGe2S6. Our work opens a new direction for research on layertronics.

Magnetic skyrmions and their manipulations in a 2D multiferroic CuCrP2Te6 monolayer.

Magnetic skyrmions and their effective manipulations are promising for the design of next-generation information storage and processing devices, due to their topologically protected chiral spin textures and low energy cost. They, therefore, have attracted significant interest from the communities of condensed matter physics and materials science. Herein, based on density functional theory (DFT) calculations and micromagnetic simulations, we report the spontaneous 2 nm-diameter magnetic skyrmions in the monolayer CuCrP2Te6 originating from the synergistic effect of broken inversion symmetry and strong Dzyaloshinskii-Moriya interactions (DMIs). The creation and annihilation of magnetic skyrmions can be achieved via the ferroelectric to anti-ferroelectric (FE-to-AFE) transition, due to the variation of the magnetic parameter D2/|KJ|. Moreover, we also found that the DMIs and Heisenberg isotropic exchange can be manipulated by bi-axial strain, to effectively enhance skyrmion stability. Our findings provide feasible approaches to manipulate the skyrmions, which can be used for the design of next-generation information storage devices.

Broadband nonlinear optical response and sub-picosecond carrier dynamics in graphene-SnSe2 van der Waals heterostructures.

The van der Waals (vdWs) heterostructures, with vertical layer stacking structure of various two-dimensional (2D) materials, maintain the reliable photonic characteristics while compensating the shortcomings of the participating individual components. In this work, we combine the less-studied multilayer tin selenide (SnSe2) thin film with one of the traditional 2D materials, graphene, to fabricate the graphene-based vdWs optical switching element (Gr-SnSe2) with superior broadband nonlinear optical response. The transient absorption spectroscopy (TAS) measurement results verify that graphene acts as the recombination channel for the photogenerated carrier in the Gr-SnSe2 sample, and the fast recovery time can be reduced to hundreds of femtoseconds which is beneficial for the optical modulation process. The optical switching properties are characterized by the I-scan measurements, exhibiting a saturable energy intensity of 2.82 mJ·cm-2 (0.425 µJ·cm-2) and a modulation depth of 15.6% (22.5%) at the wavelength of 1030 nm (1980nm). Through integrating Gr-SnSe2 with a cladding waveguide, high-performance picosecond Q-switched operation in the near-infrared (NIR) and mid-infrared (MIR) spectral regions are both achieved. This work experimentally demonstrates the great potential of graphene-based vdWs heterostructures for applications in broadband ultrafast photonics.

Layer-Polarized Anomalous Hall Effects from Inversion-Symmetric Single-Layer Lattices.

In the field of physics and materials science, the discovery of the layer-polarized anomalous Hall effect (LP-AHE) stands as a crucial development. The current research paradigm is rooted in topological or inversion-asymmetric valleytronic systems, making such a phenomenon rather rare. In this work, a universal design principle for achieving the LP-AHE from inversion-symmetric single-layer lattices is proposed. Through tight-binding model analysis, we demonstrate that by stacking into antiferromagnetic van der Waals bilayer lattices, the coupling physics between PT symmetry and vertical external bias can be realized. This coupling reveals the previously neutralized layer-locked Berry curvature, compelling the carriers to move in a specific direction within a given layer, thereby realizing the LP-AHE. Intriguingly, the chirality of the LP-AHE can be effectively switched by modulating the direction of vertical external bias. First-principles calculations validate this mechanism in bilayer T-FeCl2 and MnPSe3. Our results pave the way for new explorations of the LP-AHE.

Amorphous Vanadium Oxides with Dual ion Storage Mechanism for High-Performance Aqueous Zinc ion Batteries.

Owing to the extremely limited structural deformation caused by the introduction of guest ions that their rigid structure can sustain, crystalline materials typically fail owing to structural collapse when utilized as electrode materials. Amorphous materials, conversely, are more resistant to volume expansion during dynamic ion transport and can introduce a lot of defects as active sites. Here, The amorphous polyaniline-coated/intercalated V2O5·nH2O (PVOH) nanowires are prepared by in situ chemical oxidation combined with self-assembly strategy, which exhibited impressive electrochemical properties because of its short-range ordered crystal structure, oxygen vacancy/defect-rich, improved electronic channels, and ionic channels. Through in situ techniques, the energy storage mechanism of its Zn2+/H+ co-storage is investigated and elucidated. Additionally, this work provides new insights and perspectives for the investigation and application of amorphous cathodes for aqueous zinc ion batteries.

Electrocatalytic Urea Synthesis via N2 Dimerization and Universal Descriptor.

Electrocatalytic urea synthesis through N2 + CO2 coreduction and C-N coupling is a promising and sustainable alternative to harsh industrial processes. Despite considerable efforts, limited progress has been made due to the challenges of breaking inert N≡N bonds for C-N coupling, competing side reactions, and the absence of theoretical principles guiding catalyst design. In this study, we propose a mechanism for highly electrocatalytic urea synthesis using two adsorbed N2 molecules and CO as nitrogen and carbon sources, respectively. This mechanism circumvents the challenging step of N≡N bond breaking and selective CO2 to CO reduction, as the free CO molecule inserts into dimerized *N2 and binds concurrently with two N atoms, forming a specific urea precursor *NNCONN* with both thermodynamic and kinetic feasibility. Through the proposed mechanism, Ti2@C4N3 and V2@C4N3 are identified as highly active catalysts for electrocatalytic urea formation, exhibiting low onset potentials of -0.741 and -0.738 V, respectively. Importantly, taking transition metal atoms anchored on porous graphite-like carbonitride (TM2@C4N3) as prototypes, we introduce a simple descriptor, namely, effective d electron number (Φ), to quantitatively describe the structure-activity relationships for urea formation. This descriptor incorporates inherent atomic properties of the catalyst, such as the number of d electrons, the electronegativity of the metal atoms, and the generalized electronegativity of the substrate atoms, making it potentially applicable to other urea catalysts. Our work advances the comprehension of mechanisms and provides a universal guiding principle for catalyst design in urea electrochemical synthesis.

Indirect regulation of topsoil nutrient cycling by groundwater depth: impacts on sand-fixing vegetation and rhizosphere bacterial communities.

Introduction: The impact of groundwater table depth (GTD) on bacterial communities and soil nutrition in revegetated areas remains unclear. Methods: We investigated the impacts of plant growth and soil physicochemical factors on rhizosphere bacterial communities under different GTD. Results: The four plant growth indices (Pielou, Margalef, Simpson, and Shannon-Wiener indices) and soil water content (SWC) at the Artem and Salix sites all showed a decreasing trend with increasing GTD. Salix had a higher nutrient content than Artem. The response of plant rhizosphere bacterial communities to GTD changes were as follows. Rhizosphere bacteria at the Artem and Salix sites exhibited higher relative abundance and alpha diversity in SW (GTD < 5 m) compared than in DW (GTD > 5 m). Functional microbial predictions indicated that the rhizosphere bacterial communities of Artem and Salix promoted carbon metabolism in the SW. In contrast, Artem facilitated nitrogen cycling, whereas Salix enhanced both nitrogen cycling and phototrophic metabolism in the DW. Discussion: Mantel test analysis revealed that in the SW of Artem sites, SWC primarily governed the diversity of rhizosphere and functional bacteria involved in the nitrogen cycle by affecting plant growth. In DW, functional bacteria increase soil organic carbon (SOC) to meet nutrient demands. However, higher carbon and nitrogen availability in the rhizosphere soil was observed in the SW of the Salix sites, whereas in DW, carbon nutrient availability correlated with keystone bacteria, and changes in nitrogen content could be attributed to nitrogen mineralization. This indicates that fluctuations in the groundwater table play a role in regulating microbes and the distribution of soil carbon and nitrogen nutrients in arid environments.

Red-Light-Responsive Polypeptoid Nanoassemblies Containing a Ruthenium(II) Polypyridyl Complex with Synergistically Enhanced Drug Release and ROS Generation for Anticancer Phototherapy.

Polymer micelles/vesicles made of a red-light-responsive Ru(II)-containing block copolymer (PolyRu) are elaborated as a model system for anticancer phototherapy. PolyRu is composed of PEG and a hydrophobic polypeptoid bearing thioether side chains, 40% of which are coordinated with [Ru(2,2':6',2″-terpyridine)(2,2'-biquinoline)](PF6)2 via the Ru-S bond, resulting in a 67 wt % Ru complex loading capacity. Red-light illumination induces the photocleavage of the Ru-S bond and produces [Ru(2,2':6',2″-terpyridine)(2,2'-biquinoline)(H2O)](PF6)2. Meanwhile, ROS are generated under the photosensitization of the Ru complex and oxidize hydrophobic thioether to hydrophilic sulfoxide, causing the disruption of micelles/vesicles. During the disruption, ROS generation and Ru complex release are synergistically enhanced. PolyRu micelles/vesicles are taken up by cancer cells while they exhibit very low cytotoxicity in the dark. In contrast, they show much higher cytotoxicity under red-light irradiation. PolyRu micelles/vesicles are promising nanoassembly prototypes that protect metallodrugs in the dark but exhibit light-activated anticancer effects with spatiotemporal control for photoactivated chemotherapy and photodynamic therapy.

Controllable Electrocatalytic to Photocatalytic Conversion in Ferroelectric Heterostructures.

Photocatalytic and electrocatalytic reactions to produce value-added chemicals offer promising solutions for addressing the energy crisis and environmental pollution. Photocatalysis is driven by light excitation and charge separation and relies on semiconducting catalysts, while electrocatalysis is driven by external electric current and is mostly based on metallic catalysts with high electrical conductivity. Due to the distinct reaction mechanism, the conversion between the two catalytic types has remained largely unexplored. Herein, by means of density functional theory (DFT) simulations, we demonstrated that the ferroelectric heterostructures Mo-BN@In2Se3 and WSe2@In2Se3 can exhibit semiconducting or metallic features depending on the polarization direction as a result of the built-in field and electron transfer. Using the nitrogen reduction reaction (NRR) and hydrogen evolution reaction (HER) as examples, the metallic heterostructures act as excellent electrocatalysts for these reactions, while the semiconducting heterostructures serve as the corresponding photocatalysts with improved optical absorption, enhanced charge separation, and low Gibbs free energy change. The findings not only bridge physical phenomena of the electronic phase transition with chemical reactions but also offer a new and feasible approach to significantly improve the catalytic efficiency.

Bloch-type magnetic skyrmions in two-dimensional lattices.

Magnetic skyrmions in two-dimensional lattices are a prominent topic of condensed matter physics and materials science. Current research efforts in this field are exclusively constrained to Néel-type and antiskyrmions, while Bloch-type magnetic skyrmions are rarely explored. Here, we report the discovery of Bloch-type magnetic skyrmions in a two-dimensional lattice of MnInP2Te6, using first-principles 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-of-plane magnetic anisotropy, gives rise to skyrmion physics in monolayer MnInP2Te6, in the absence of a magnetic field. Remarkably, different from all previous works on two-dimensional lattices, the resultant magnetic skyrmions feature Bloch-type magnetism, which is protected by D3 symmetry. Furthermore, Bloch-type magnetic bimerons are also identified in monolayer MnTlP2Te6. The phase diagrams of these Bloch-type topological magnetisms under a magnetic field, temperature and strain are mapped out. Our results greatly enrich the research on magnetic skyrmions in two-dimensional lattices.

Ferroelectrically tunable magnetic skyrmions in two-dimensional multiferroics.

Magnetic skyrmions are topologically protected entities that are promising for information storage and processing. Currently, an essential challenge for future advances of skyrmionic devices lies in achieving effective control of skyrmion properties. Here, through first-principles and Monte-Carlo simulations, we report the identification of nontrivial topological magnetism in two-dimensional multiferroics of Co2NF2. Because of ferroelectricity, monolayer Co2NF2 exhibits a large Dzyaloshinskii-Moriya interaction. This together with exchange interaction can stabilize magnetic skyrmions with the size of sub-10 nm under a moderate magnetic field. Importantly, arising from the magnetoelectric coupling effect, the chirality of magnetic skyrmions is ferroelectrically tunable, producing the four-fold degenerate skyrmions. When interfacing with monolayer MoSe2, the creation and annihilation of magnetic skyrmions, as well as phase transition between skyrmion and skyrmion lattice, can be realized in a ferroelectrically controllable fashion. A dimensionless parameter κ' is further proposed as the criterion for stabilizing magnetic skyrmions in such multiferroic lattices. Our work greatly enriches the two-dimensional skyrmionics and multiferroics research.

Layer Hall Effect in Multiferroic Two-Dimensional Materials.

The layer Hall effect (LHE) is of fundamental and practical importance in condensed-matter physics and material science; however, it was rarely observed and usually based on the paradigms of persistent electric field and sliding ferroelectricity. Here, a new mechanism of LHE is proposed by coupling layer physics with multiferroics using symmetry analysis and a low-energy k·p model. Due to time-reversal symmetry breaking and valley physics, the Bloch electrons on one valley will be subject to a large Berry curvature. This combined with inversion symmetry breaking gives rise to layer-polarized Berry curvature and can force the electrons to deflect in one direction of a given layer, thereby generating the LHE. We demonstrate that the resulting LHE is ferroelectrically controllable and reversible. Using first-principles calculations, this mechanism and predicted phenomena are verified in the multiferroic material of bilayer Co2CF2. Our finding opens a new direction for LHE and 2D materials research.

Nonvolatile electro-mechanical coupling in two-dimensional lattices.

Electro-mechanical coupling is of great interest for applications in sensors, actuators and energy harvesters. While the control of electrical charge by mechanical force has been studied extensively, reverse coupling is rarely explored, especially in two-dimensional (2D) lattices. Herein, we propose a novel mechanism for electro-mechanical coupling that realizes the electric field switching of the dimensions of a 2D lattice in a reversible and nonvolatile fashion, through the mediated strength of interlayer interactions in ferroelectric bilayer systems. Based on first-principles calculations, the validity of this mechanism is demonstrated in a series of real bilayer materials, i.e., MoS2/ReIrGe2S6, Sb/In2Se3 and bilayer In2Se3. The interface differences due to polarization play a crucial role in realizing such nonvolatile electro-mechanical coupling, and the underlying physical origin is discussed. These explored phenomena and insights offer a novel avenue for the highly desired nonvolatile electric field control of mechanical strain.

Activating dual atomic electrocatalysts for the nitric oxide reduction reaction through the P/S element.

The development of efficient atomic electrocatalysts to resolve the activity and selectivity issues of the nitric oxide reduction reaction (NORR) has increasingly received more attention but is still challenging. The current research on the dual atomic NORR electrocatalyst is exclusively focused on TM atoms. Herein, we propose a novel mechanism of introducing a P/S element, which takes advantage of finite orbitals to active the transition metal (TM) atoms of dual atomic electrocatalysts for NORR. The finite orbitals can hinder the capture of the lone pair electrons of NO but modulate the electronic configurations of the neighboring TM and thus the "donation-backdonation" mechanism can be realized. Through large-scale first-principles calculations, the catalytic performance of a series of P/S-TM biatoms supported by the monolayer CN (P/S-TM@CN) is evaluated. According to a "four-step" screening strategy, P-Cu@CN and S-Ni@CN are successfully screened as promising catalysts with outstanding activity and high selectivity for direct NO-to-NH3 conversion. Moreover, we identify Δεd-p as a valid descriptor to evaluate the adsorption of NO on such catalysts, allowing for reducing the number of catalytic candidates. Our work thus provides a new direction for the rational design of dual atomic electrocatalysts.

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 MnTe2/ZrS2. Arising from interlayer coupling, MnTe2/ZrS2 can harbor a large Dzyaloshinskii-Moriya interaction. This, combined with exchange interaction, yields an intriguing skyrmion phase under a tiny magnetic field of 75 mT. Meanwhile, upon harnessing a small electric field, magnetic bimeron can be observed in MnTe2/ZrS2, suggesting the existence of multiple topological magnetism. Through interlayer sliding, both topological magnetisms can be switched on-off. In addition, the impacts of d∥ and Keff on these spin textures are revealed, and a dimensionless parameter κ 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.

Layer-polarized anomalous Hall effects in valleytronic van der Waals bilayers.

The layer-polarized anomalous Hall effect (LP-AHE), derived from the coupling between the Berry curvature and the 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 a phenomenon rather scarce. Here, through model analysis, we propose an alternative, but general, mechanism for realizing the LP-AHE in valleytronic van der Waals bilayers by interlayer sliding. The interaction between out-of-plane ferroelectricity and A-type antiferromagnetism gives rise to the layer-locked Berry curvature and thus the long-sought LP-AHE in bilayer systems. The LP-AHE can be strongly coupled with sliding ferroelectricity, rendering it 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 the LP-AHE and explore its application in electronics.

Theoretical Prediction of Antiferromagnetic Skyrmion Crystal in Janus Monolayer CrSi2N2As2.

An antiferromagnetic skyrmion crystal (AF-SkX), a regular array of antiferromagnetic skyrmions, is a fundamental phenomenon in the field of condensed-matter physics. So far, very few proposals have been made to realize the AF-SkX, and most have been based on three-dimensional (3D) materials. Herein, using first-principles calculations and Monte Carlo simulations, we report the identification of AF-SkX in a two-dimensional lattice of the Janus monolayer CrSi2N2As2. Arising from the broken inversion symmetry and strong spin-orbit coupling, a large Dzyaloshinskii-Moriya interaction is obtained in the Janus monolayer CrSi2N2As2. This, combined with the geometric frustration of its triangular lattice, gives rise to the skyrmion physics and long-sought AF-SkX in the presence of an external magnetic field. More intriguingly, this system presents two different antiferromagnetic skyrmion phases, and such a phenomenon is distinct from those reported in 3D systems. Furthermore, by contacting with Sc2CO2, the creation and annihilation of AF-SkX in Janus monolayer CrSi2N2As2 can be achieved through ferroelectricity. These findings greatly enrich the research on antiferromagnetic skyrmions.

Spontaneous Valley Polarization and Electrical Control of Valley Physics in Single-Layer TcIrGe2S6.

The modulation of valley polarization in one single system is of important fundamental and practical importance in quantum information technology. Here, through the first-principles calculations, we identify single-layer TcIrGe2S6 as a tantalizing candidate for realizing the modulation of valley polarization. Arising from the combination of inversion symmetry breaking and intrinsic magnetic exchange interaction, single-layer TcIrGe2S6 exhibits spontaneous valley polarization. The value of valley polarization in the conduction band is 161 meV, favorable for achieving the intriguing anomalous valley Hall effect. Furthermore, single-layer TcIrGe2S6 possesses ferroelectric order. More remarkably, its ferroelectric and valley physics can be strongly coupled, namely, the valley properties can be switched off and on electrically. These findings not only provide a compelling candidate for two-dimensional valleytronic research but also open a new avenue for modulating valley physics.

Spontaneous Magnetic Skyrmions in Single-Layer CrInX3 (X = Te, Se).

The realization of magnetic skyrmions in nanostructures holds great promise for both fundamental research and device applications. Despite recent progress, intrinsic magnetic skyrmions in two-dimensional lattice are still rarely explored. Here, using first-principles calculations and Monte Carlo simulations, we report the identification of spontaneous magnetic skyrmions in single-layer CrInX3 (X = Te, Se). Because of the joint effect of broken inversion symmetry and strong spin-orbit coupling, inherent large Dzyaloshinskii-Moriya interaction occurs in both systems, endowing the intriguing Néel-type skyrmions. By further imposing moderate magnetic field, the skyrmion phase can be obtained and is stable within a wide temperature range. Particularly for single-layer CrInTe3, the size of skyrmions is sub-10 nm and the skyrmion phase can be maintained at an elevated temperature of ∼180 K. In addition, the phase diagrams of their topological spin textures under the variation of magnetic parameters of D, J, and K are mapped out.