Compensated ferrimagnets have attracted significant interest because their nearly zero net magnetization eliminates stray fields, enabling dense, interference-free integration of spintronic devices. So far, most research on compensated ferrimagnets has focused on thin films of ferrimagnetic alloys containing rare-earth and transition-metal elements. Here, we demonstrate that yttrium iron garnets with Er substitution, Y3-xErxFe5O12, exhibit unique ferrimagnetic properties, with magnetization compensation points (MCPs) that can be modulated by Er contents. The Y3-xErxFe5O12 shows ferrimagnetic behavior with nearly compensated magnetization near zero at TMCP, which varies linearly with Er contents. Additionally, the temperature-dependent magnetic hysteresis of the Y3-xErxFe5O12 taken near the TMCP shows 40-100 times enhanced coercive fields. These newly discovered compensated ferrimagnetic behaviors in Er-yttrium iron garnet pave the way for the development of ultrafast, low-power spintronics devices that aim to utilize antiferromagnetically coupled spin sublattices.

Charge density waves (CDWs) involve coupled amplitude and phase degrees of freedom, but direct access to local amplitude correlations remains experimentally challenging. Here, we report cryogenic four-dimensional scanning transmission electron microscopy measurements of CDW ordering in a 2 H − NbSe 2 flake of 24 nm thickness, enabled by liquid-helium-based cooling. By mapping the spatial distribution of CDW superlattice intensities at nanometer-scale resolution and analyzing their autocorrelations, we extract the temperature-dependent correlation length associated with the local amplitude of the CDW order parameter, independent of global phase coherence. Our results reveal that a finite local CDW amplitude is already established well above the transition temperature. When the system is cooled below the transition temperature down to 20 K, the correlation length extends to nearly 110 nm, and the local CDW amplitude is found to strongly anticorrelate with the local strain field.

Magnetism in van der Waals (vdW) materials offers a platform for exploring dimensionality-tuned magnetic ordering and distinct spin-phonon coupling. Among such materials, CrPS4 stands out as an air-stable A-type antiferromagnet with a Néel temperature of 36 K. Here, we investigate the evolution of phonon modes influenced by magnetic ordering in CrPS4 across varying temperatures and layer thicknesses by using Raman spectroscopy, supported by theoretical calculations. Due to weak interlayer coupling, the thickness-dependent changes in phonon frequencies are negligible (<0.5 cm-1). Notably, anomalous temperature-dependent behavior of the nominally non-magnetic P-S rocking mode reveals its coupling to Cr-S-Cr super-exchange pathways, indicating a strong spin-phonon interaction in CrPS4. The observed magnetic order and spin-phonon interactions remain robust across different thicknesses, with coupling strengths comparable to those of other vdW magnets. Magneto-crystalline anisotropy, metamagnetic transitions, and strong spin-phonon coupling highlight CrPS4 as a promising candidate for integration into vdW heterostructures, offering potential for next-generation magnetic device applications.

We demonstrate room-temperature nucleation and manipulation of topological spin textures in the van der Waals (vdW) ferromagnet Fe3GaTe2 using laser-pulse excitation. Rapid laser-induced heating followed by cooling enables access to the skyrmion bubble state at low fields and drives reversible switching between this state and labyrinth domains. The switching requires a minimum of about 20 pulses, and further reduction of the pulse number is limited by sample degradation at higher fluence. The nucleation occurs at magnetic induction fields as low as 5 mT, which substantially lowers the field requirement compared to slow field-cooling approaches. Micromagnetic simulations attribute this switching to the thermal cycle induced by the laser. Our findings establish vdW ferromagnets as promising candidates for room-temperature, laser-controlled, non-volatile memory storage applications.

van der Waals (vdW) layered semiconductors have emerged as a unique class of quantum materials distinguished from their bulk counterparts by reduced dielectric screening, strong Coulomb interactions, large exciton binding energies, strong spin-orbit coupling, and pronounced thickness-dependent band structures. These fundamental attributes have enabled the exploration of exotic many-body physics and a broad spectrum of device applications, ranging from field-effect transistors and ferroelectric switches to optoelectronics, magnetic semiconductors, neuromorphic computing, and energy harvesting systems. Despite remarkable advances, critical challenges remain in the controlled synthesis of high-quality crystals, formation of low-resistance contacts, integration of stable and scalable gate dielectrics, and reliable device performance at the wafer scale. In this mega-review, we provide a comprehensive overview of contemporary challenges and future opportunities in vdW-layered semiconductors, structured across nine themes: growth and heterostructures of transition metal dichalcogenides, Ohmic contacts, emerging gate dielectrics, high-performance low-power field-effect transistors (FETs), diluted magnetic semiconductors, plasmonics and exciton propagation, hot-carrier solar cells, bioinspired neuromorphic computing, and electrocatalytic/photocatalytic energy conversion. By consolidating fundamental insights and device-level perspectives, this review aims to chart a roadmap for advancing vdW semiconductors from laboratory-scale discoveries to transformative technologies in electronics, optoelectronics, spintronics, and sustainable energy systems.

We report the intrinsic thermal and magnetic properties of the low-dimensional van der Waals (vdW) antiferromagnet NiPS_3 and explore its emergent magnetic phases by controlling crystallographic twinning. Using nearly twin-free crystals, we resolve intrinsic properties that are typically obscured by multidomain effects in bulk samples. Magnetization results reveal a highly anisotropic, sharp spin-flop transition, confirming the high domain purity of our crystals. Furthermore, high-precision thermodynamic and transport data reveal a broad fluctuation regime around the Néel temperature (T_N = 157.5 K), with a heat capacity anomaly and a concurrent suppression of thermal conductivity. Field-dependent thermal transport shows a small but distinct contribution from spin-lattice coupling, as evidenced by the dip at the spin-flop transition. We develop a theoretical model to explain these properties reported in this paper, with good agreement between experiment and theory. Our work establishes a definitive baseline for bulk properties of NiPS_3 and demonstrates the feasibility of resolving intrinsic anisotropies by addressing crystallographic twinning in vdW magnets.

Since the invention of the first transistor based on germanium, a wide range of 3D semiconductors, metals and insulators have been used as building blocks for integrated logic and memory devices. However, the energy consumption of electronic devices based on these 3D materials has continued to increase, particularly in emerging paradigms such as artificial intelligence, raising concerns about the long-term sustainability of technological advancement. To overcome this limitation, incorporating atomically thin van der Waals materials into electronic devices has been proposed, as their unique structural, electronic and polymorphic properties could enable new mechanisms to enhance device energy efficiency. Here, we discuss fundamental challenges faced by conventional 3D-material-based electronics and present how van der Waals materials can be used to address these limitations for energy-efficient device architectures. We conclude by summarizing the key challenges that remain and outlining strategic directions to bridge the gap between fundamental materials science and practical device applications for sustainable, energy-efficient devices. Emerging applications, including artificial intelligence, are associated with increasing energy consumption, posing fundamental challenges to the long-term sustainability of current electronic devices. This Review discusses key metrics for energy efficiency and explores how the unique structural, electronic and polymorphic properties of van der Waals materials enable new device strategies.

Metal (1T/1T')-semiconductor (2H) phase transition memristors (PTMEMs) based on intercalated alkali metal ions (Li+) in transition metal dichalcogenides (TMDs) exhibit excellent electrical properties, including heterosynaptic plasticity. However, the low stability of Li+ ions limits retention and on/off ratios of the PTMEMs. Here, a phase transition in MoTe2 induced by intercalated Ag+ ions is demonstrated for the first time, enabling robust memristor operation. The migration of Ag+ ions, controlled by voltage biases, clearly realizes reversible 2H-1T/1T' phase transitions, as revealed by transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman mapping. The memristive mechanism of MoTe2 shifts from doping (4-8 h) to phase transition (12 h) as Ag intercalation time increases, achieving a 200 000 on/off ratio at a 4 nm thickness. MoTe2 exhibits the most evident phase transition due to its low transition barrier (0.84) compared to other TMDs (>1.22). Intercalated Ag+ ions provide outstanding memristive performance over Li+ ions, with a 100 times higher on/off ratio, 300 times better retention, and 8 times lower non-linearity (βAg = 0.5-0.6, βLi = 4.0). Ag+MoTe2 PTMEM achieves 91.7% accuracy in MNIST recognition, surpassing the 81.7% accuracy of Li+MoS2 PTMEM. These findings demonstrate that Ag+MoTe2 PTMEM holds great potential for advanced memory-based neural network applications.

Alkali ions are crucial to physiological neural activitiesand their dynamics can be implemented in various iontronics. For the host materials for al preferred choice thanks to their facilitating ion Nevertheless, challenges such as the need for exte and thermodynamic stability during ion movem understanding of the electrical dynamics associated with alkali ion movement has rarely been demonstrated in 2D layered materials so far. Here, layered MnO2 nanoplate with potassium ions combination of potassium ions and layered MnO2 with a subsequent phase transition, resulting in material's distinct hybrid plasticity, driven by its i sequential motion recognition, valuable for ass kali ions, 2D layered materials have become the accommodation and movement between layers. r nal electrolytes, pre-fabrication for ion intercalation, ents still persist. Consequently, the comprehensive we engineered an electrolyte-free high-crystalline 2D by metal-organic chemical vapor deposition. The exhibits electrically induced ion migration coupled negative differential resistance. Furthermore, the on dynamics, provides a sophisticated platform for essing continuous motion across varied subjects. Finally, we demonstrate the broad applicability spatiotemporal ion modulation within three-t advancements. of our 2D K-MnO2 and highlight its versatility in erm inal structures, showing potential for future

Fabricating disordered solids at atomic-scale thickness at the desired area is challenging because of the high energy cost of weakening the covalent bonds. Here, we demonstrate a low-power laser-patterning of a transparent amorphous phase on a two-dimensional transition metal chalcogenide alloy. Laser irradiation induces selective evaporation of elements in the crystalline 2H-Mo0.92W0.08Te2 (c-2H), resulting in the progressive phase transformation from crystalline 2H to amorphous MoWTe (a-MoWTe) phase with an intermediate polycrystalline 1T'-Mo0.92W0.08Te2-x (p-1T'). The a-MoWTe has multi-valent cations of Mo5+, W4+, and W6+, indicating that the local chemical environments of a-MoWTe are different from those of c-2H. The multi-valence states of cations could result in a significant lattice disorder by changing the coordination numbers, leading to the phase transformation from crystalline to amorphous phase. Our laser-patterned 2D amorphous phase enables a practical application for next-generation nanoelectronics and photonics, energy storage/conversion, and sensors.

While phase change devices have emerged as promising candidates for implementing artificial synapses, conventional phase change materials have faced challenges such as high-power consumption and limited reliability, originating from their Joule heating-driven phase transition mechanisms. Here, a phase change device based on a 2D material, Mo0.95W0.05Te2 is demonstrated, which exhibits a phase transition between semiconducting 2H and semimetallic 1T' structural phases, facilitated by a ferroelectric substrate. The structural phase transitions are confirmed by Raman spectroscopy under drain or gate voltage bias. These bias conditions allow two types of operation to be realized in a single device structure, resulting in gate voltage modulation and drain voltage modulation with a ferroelectric substrate. The ferroelectric-induced phase change device exhibits key synaptic functions, including short-term and long-term plasticity, along with highly linear and symmetric multilevel conductance states. Furthermore, polymorphic Mo0.95W0.05Te2 enables energy consumption as low as 5.3 pJ per switching event at monolayer thickness beyond conventional 3D phase change memory. These features highlight the potential of 2D material-based phase change devices on ferroelectric substrates as energy-efficient and high-performance components for next-generation neuromorphic computing systems.

A single-crystalline system typically stabilizes a unique state for spin ordering below a critical temperature. Certain materials exhibit multiple magnetic states, often driven by structural phase transitions under varying thermodynamic conditions. Recently, van der Waals magnets have demonstrated subtle interlayer exchange interactions, offering a promising approach to control spin and correlated states. Here, we report the emergence of three distinct magnetic states─ferromagnetic ordering and both collinear and noncollinear antiferromagnetic orderings─in a layered single-crystalline magnet, cobalt-doped Fe3GaTe2 ((Co, Fe)3GaTe2). These three magnetic phases can be observed in a single material, a phenomenon we designate as polymorphic spin ordering in the material. The introduction of 16% Co-doping in Fe3GaTe2 modulates the interlayer magnetic interaction, enabling multiple spin orderings within the same lattice system with three critical temperatures: a Curie temperature for a ferromagnetic state (Tc = 210 K) and two Néel temperatures for the collinear (TN1 = 110 K) and noncollinear (TN2 = 30 K) antiferromagnetic states. Our findings, supported by magnetic force microscopy, first-principles calculations, and circular dichroism angular photoemission spectroscopy, reveal varying spin ordering and abrupt changes in the topological band structure and Berry curvature within single-crystalline (Co, Fe)3GaTe2.

Designing magnetic van der Waals (vdW) heterostructures by stacking two-dimensional (2D) magnetic materials with other 2D materials enables the investigation of 2D spintronics owing to the strong magnetic proximity effect. Spin manipulation at the vdW interface can be achieved by stacking architectures and external stimuli, such as magnetic fields, electric fields, stress, and light. Moreover, elucidating the effects of magnetic interfacial interactions and related interlayer coupling is crucial for exploring practical spintronic applications of magnetic vdW heterostructures. In this review, vdW interlayer interactions are categorized into spin–orbit coupling, spin transfer torque, and spin–charge transfer, and the magnetic vdW heterostructures are classified into three categories: magnetic material/magnetic material, magnetic material/non-magnetic material, and magnetic material/ferroelectric material heterostructures. Subsequently, related interfacial interactions in magnetic vdW heterostructures are introduced, and the spin manipulation technique is discussed. Moreover, various applications of magnetic vdW heterostructures by modulating the electron spin are explored. Finally, emerging opportunities are highlighted, and a perspective on the future development of magnetic vdW heterostructures through delicate spin manipulation is provided. Magnetic vdW heterostructures are classified according to vdW interlayer interactions including spin-orbit coupling, spin-transfer torque, and spin-charge transfer. Various applications and perspectives of magnetic vdW heterostructures allow authors to explore novel applications through spin manipulation.

This study investigates the applicability of the machine learning model in correlative spectroscopy to enhance spatial resolution for probing nanoscale structural perturbations. The developed model demonstrates significant enhancement in spatial resolution, achieving up to 50 nm through the integration of Kelvin probe force microscopy and atomic force microscopy data. The predicted nanoscale Raman image reveals abnormal behaviors associated with strain-induced lattice perturbations, such as the presence of compressive and tensile strains within identical nanoscale wrinkles. Afterward, we interpreted the trained model using explainable artificial intelligence techniques, uncovering synergistic contributions to the Raman features across each input dataset within the nanoscale region. Our analysis demonstrates that the model effectively reflects key strain-induced lattice behaviors, highlighting its nanoscale sensitivity to structural perturbations. Finally, we validated these findings using quantum mechanical calculations, which confirmed the strain-induced changes in Raman-active modes. This study offers comprehensive insights into nanoscale structural perturbations, paving the way for innovative approaches to high-resolution spectroscopic analysis in low-dimensional materials.

Scanning probe microscopy (SPM) has become a valuable tool for probing physical properties and nanoscale materials and devices. However, conventional SPM imaging requires manual identification of regions of interest and heavily depends on human intuition for image interpretation, which severely limits the ability to collect large datasets and conduct objective analysis. In this work, an AI‐assisted autonomous SPM framework is presented for microstructural and electrical property characterization of 2D materials with high efficiency. By analyzing topographic features through advanced clustering algorithms, the approach employs accurate image segmentation of complex geometries and multilevel thickness variations in overlapping 2D MoWTe2 flakes. To demonstrate its scalability, this autonomous workflow is applied to over 100 MoWTe2 flakes. Levering SPM's multimodal imaging capabilities, the framework simultaneously extracts flake thickness and work function, allowing for direct correlation between these properties. This deep‐learning‐driven autonomous approach mitigates the need for manual intervention, significantly accelerating the exploration and characterization of nanomaterials across diverse material systems.

Marginally twisted bilayer graphene with large Bernal stacked domains involves symmetry-breaking features with domain boundaries that exhibit topological edge states normally obscured by trivial bands. A vertical electric field can activate these edge states through inversion symmetry breaking and opening a bandgap around the edge state energy. However, harnessing pristine topological states at the Fermi level without violent electric or magnetic bias remains challenging, particularly above room temperature. Here, we demonstrate that thermal biasing can break the vertically stacked lattice symmetry of twisted bilayer graphene via the interatomic Seebeck effect, enabling thermoelectric imaging of topological edge states at tunable Fermi levels above room temperature. The high spatial resolution in the imaging is achieved through atomic-scale thermopower generation between a metallic tip and the sample, reflecting the local electronic band structure and its derivative features of twisted bilayer graphene at the Fermi level. Our findings suggest that thermal biasing provides a sensitive, non-destructive method for symmetry breaking and topological state imaging above room temperature, making it a practical and accessible approach.

While phase change devices have emerged as promising candidates for implementing artificial synapses, conventional phase change materials have faced challenges such as high‐power consumption and limited reliability, originating from their Joule heating‐driven phase transition mechanisms. Here, a phase change device based on a 2D material, Mo 0.95 W 0.05 Te 2 is demonstrated, which exhibits a phase transition between semiconducting 2H and semimetallic 1T’ structural phases, facilitated by a ferroelectric substrate. The structural phase transitions are confirmed by Raman spectroscopy under drain or gate voltage bias. These bias conditions allow two types of operation to be realized in a single device structure, resulting in gate voltage modulation and drain voltage modulation with a ferroelectric substrate. The ferroelectric‐induced phase change device exhibits key synaptic functions, including short‐term and long‐term plasticity, along with highly linear and symmetric multilevel conductance states. Furthermore, polymorphic Mo 0.95 W 0.05 Te 2 enables energy consumption as low as 5.3 pJ per switching event at monolayer thickness beyond conventional 3D phase change memory. These features highlight the potential of 2D material‐based phase change devices on ferroelectric substrates as energy‐efficient and high‐performance components for next‐generation neuromorphic computing systems.

Nickel ditelluride (NiTe2), one of the group-10 transition metal dichalcogenides, has shown intriguing surface states originating from its topological semimetallicity. Here, we demonstrate abnormal catalytic activities at the NiTe2 surface for the hydrogen evolution reaction (HER). We investigate the differences in catalytic activities at the basal and edge planes of NiTe2 using a micro-sized electrochemical reactor. The basal plane is found to be more active than the edge plane, resulting in a current density at the basal plane of NiTe2 exceeding 700 mA/cm2 with a small overpotential of -0.162 V. Interestingly, our ab initio calculations show a discrepancy with the experimental measurements, indicating that the crystal-orientation-dependent HER activity highlights the unique characteristics of a topological semimetal, which can significantly influence the HER in NiTe2 catalysts.

As the dimension of electronic devices shrinks to electronic screening lengths (<10 nm), electric polarization becomes critical for device performance. Electric polarization has been widely investigated in ferroelectric devices, where nonvolatile polarization switching occurs in ferroelectric dielectrics. Recently, 2D ferroelectric conductors have been discovered, enabling the switching of direct current flow through atomically thin ferroelectric channels. However, elucidating and harnessing the role of nonvolatile polarization switching in transport through ferroelectric channels and atomic-scale interfaces remain challenging. Here, we report switchable polar ohmic contacts and channels formed with 2D ferroelectric WTe2 and their impact on nonvolatile switching operation. Beyond conventional device control through carrier density and mobility, the polar 2D channel modulates the proximity effect with metal electrodes, resulting in 390 times larger switching performance than solely gating the ferroelectric channel in a two-terminal geometry. Our study highlights the potential of controlling polar ohmic contacts to overcome short-channel effects and enable multiple conductance states for neuromorphic devices.