A Perspective on Tellurium/Selenium-Based Nanomaterials for Neuromorphic Computing.

Van der Waals (vdW) materials consisting of two-dimensional (2D) building blocks have strong in-plane covalent bonding and weak interlayer interactions. While monolayer 2D materials exhibit impressive fracture resistance, as demonstrated in hexagonal boron nitride (h-BN), preserving these remarkable properties in vdW materials remains a challenge. Here we reveal an anomalous mechanical interlayer coupling that involves interlayer-friction toughening and edge-reconstruction embrittlement during the fracture of multilayer h-BN. Both asynchronous and synchronous fracture modes and their flaw-size dependence are identified. Edge reconstruction in the synchronous fracture mode can eliminate a toughening mechanism induced by lattice asymmetry in monolayer h-BN, leading to embrittlement of the multilayer h-BN, while the asynchronous fracture mode results in greater fracture resistance. Such findings will provide fundamental guidelines for engineering interlayer interactions in vdW materials including heterostructures and layered architectures for better mechanical and functional performances.

Germanene, a 2D honeycomb germanium crystal, is grown at graphene/Ag(111) and hexagonal boron nitride (h‐BN)/Ag(111) interfaces by segregating germanium atoms. A simple annealing process in N2 or H2/Ar at ambient pressure leads to the formation of germanene, indicating that an ultrahigh‐vacuum condition is not necessary. The grown germanene is stable in air and uniform over the entire area covered with a van der Waals (vdW) material. As an important finding, it is necessary to use a vdW material as a cap layer for the present germanene growth method since the use of an Al2O3 cap layer results in no germanene formation. The present study also proves that Raman spectroscopy in air is a powerful tool for characterizing germanene at the interfaces, which is concluded by multiple analyses including first‐principles density functional theory calculations. The direct growth of h‐BN‐capped germanene on Ag(111), which is demonstrated in the present study, is considered to be a promising technique for the fabrication of future germanene‐based electronic devices.

Origins of heat transport anisotropy in MoTe2 and other bulk van der Waals materials

Many fascinating properties and applications of van der Waals (vdW) materials arise from how their layers slide against each other. Quantifying friction at the nanoscale is essential for further advancing the assembling of sophisticated heterostructures and their applications. A unified model and experimental validation for such friction forces remain elusive. A simple linear relationship between friction force and the energy barrier encountered by an atomic force microscope (AFM) tip interacting with crystal atoms has been proposed but not experimentally validated. Here, we present a unified understanding of nanoscale friction in vdW materials through lateral force microscopy measurements using a single AFM tip on four commonly studied vdW materials: MoS2, MoSe2, WS2, and graphene. Remarkably, the measured friction not only follows a proportional relationship with respect to the energy barriers calculated using the Lennard-Jones potential but agrees with predicted values within 5% across all examined materials. This agreement is achieved by accounting for variations in the number of contact-edge tip atoms that likely settle simultaneously into hollow sites in each material. Our findings provide critical insights to support a wide range of research efforts that rely on an advanced understanding of nanotribology in vdW materials.

The exploration of van der Waals (vdW) materials, renowned for their unique optical properties, is pivotal for advanced photonics. These materials exhibit exceptional optical anisotropy, both in-plane and out-of-plane, making them an ideal platform for novel photonic applications. However, the manual search for vdW materials with giant optical anisotropy is a labor-intensive process unsuitable for the fast screening of materials with unique properties. Here, we leverage geometrical and machine learning (ML) approaches to streamline this search, employing deep learning architectures, including the recently developed Atomistic Line Graph Neural Network. Within the geometrical approach, we clustered vdW materials based on in-plane and out-of-plane birefringence values and correlated optical anisotropy with crystallographic parameters. The more accurate ML model demonstrates high predictive capability, validated through density functional theory and ellipsometry measurements. Experimental verification with 2H-MoTe2 and CdPS3 confirms the theoretical predictions, underscoring the potential of ML in discovering and optimizing vdW materials with unprecedented optical performance.

Recent progress in strong spin-orbit coupling van der Waals materials and their heterostructures for spintronic applications

Flexible transparent InZnO synapse transistor based on Li1.3Al0.3Ti0.7(PO4)3/polyvinyl pyrrolidone nanocomposites electrolyte film for neuromorphic computing

Brain-inspired neuromorphic computing has been extensively researched, taking advantage of increased computer power, the acquisition of massive data, and algorithm optimization. Neuromorphic computing requires mimicking synaptic plasticity and enables near-in-sensor computing. In synaptic transistors, how to elaborate and examine the link between microstructure and characteristics is a major difficulty. Due to the absence of interlayer shielding effects, defect-free interfaces, and wide spectrum responses, reducing the thickness of organic crystals to the 2D limit has a lot of application possibilities in this computing paradigm. This paper presents an update on the progress of 2D organic crystal-based transistors for data storage and neuromorphic computing. The promises and synthesis methodologies of 2D organic crystals (2D OCs) are summarized. Following that, applications of 2D OCs for ferroelectric non-volatile memory, circuit-type optoelectronic synapses, and neuromorphic computing are addressed. Finally, new insights and challenges for the field’s future prospects are presented, pushing the boundaries of neuromorphic computing even farther.

Neuromorphic computing, which involves the creation of artificial synapses capable of mimicking biological brain activity, has intrigued researchers in the field of artificial intelligence (AI). To advance neuromorphic computing, a highly efficient 2D material-based artificial synapse capable of performing logical and arithmetic operations must be developed. However, fabricating large, uniform films or high-quality structures of 2D materials remains challenging because of their multistep and complex fabrication processes. In the present study, to produce large (Ø ≈ 3 in.), uniform, transparent neuromorphic devices, a novel single-step approach called proximity vapor transfer (PVT) that utilizes van der Waals (vdW) materials is employed. This single-step technique, which involves the fabrication of vdW materials on various substrates (glass, ITO, AZO, Mo, and Cu), allows control of the thickness and bandgap tunability. The Schottky device developed via the PVT method using vdW SnS with neurotransmitter (acetylcholine)-like functionality emulates biological synapses and exhibits photoelectronic synaptic behavior with wide-field-of-view synaptic plasticity. In addition, logic gate operations (NOT, OR, AND), reward-cascade neurotransmission, and imaging can be performed using 3 × 3 arrays of the device. This study represents a significant step toward the development of transparent and large-area synaptic devices, which are crucial for advancing AI applications.

Magnetic van der Waals (vdW) materials have emerged as promising candidates for spintronics applications, especially after the recent discovery of intrinsic ferromagnetism in monolayer vdW materials. There has been a critical need for tunable ferromagnetic vdW materials beyond room temperature. Here, we report a real-space imaging study of itinerant ferromagnet Fe3GeTe2 and the enhancement of its Curie temperature well above ambient temperature. We find that the magnetic long-range order in Fe3GeTe2 is characterized by an unconventional out-of-plane stripe-domain phase. In Fe3GeTe2 microstructures patterned by a focused ion beam, the out-of-plane stripe domain phase undergoes a surprising transition at 230 K to an in-plane vortex phase that persists beyond room temperature. The discovery of tunable ferromagnetism in Fe3GeTe2 materials opens up vast opportunities for utilizing vdW magnets in room-temperature spintronics devices.

Owing to the controllable growth and large-area synthesis for high-density integration, interest in employing atomically thin two-dimensional (2D) transition-metal dichalcogenides (TMDCs) for synaptic transistors is increasing. In particular, substitutional doping of 2D materials allows flexible modulation of material physical properties, facilitating precise control in defect engineering for eventual synaptic plasticity. In this study, to increase the switch ratio of synaptic transistors, we selectively performed experiments on WS2 and introduced niobium (Nb) atoms to serve as the channel material. The Nb atoms were substitutionally doped at the W sites, forming a uniform distribution across the entire flakes. The synaptic transistor devices exhibited an improved switch ratio of 103, 100 times larger than that of devices prepared with undoped WS2. The Nb atoms in WS2 play crucial roles in trapping and detrapping electrons. The modulation of channel conductivity achieved through the gate effectively simulates synaptic potentiation, inhibition, and repetitive learning processes. The Nb-WS2 synaptic transistor achieves 92.30% recognition accuracy on the Modified National Institute of Standards and Technology (MNIST) handwritten digit dataset after 125 training iterations. This study’s contribution extends to a pragmatic and accessible atomic doping methodology, elucidating the strategies underlying doping techniques for channel materials in synaptic transistors.

Research on the quantum nature of matter and light has flourished in recent years, as the field has grown for theorists and experimentalists alike. New research directions, such as the study of novel phases in quantum materials, have laid the ground for new foundational theories and future quantum technologies. In particular, novel topological materials and superconducting hybrid systems are promising for the development of novel superconductors and quantum computers. This Focus Issue aims to highlight some of the latest achievements in the field of quantum matter. It includes 3 Reviews, 1 Perspective, and 3 Research Articles on a range of topics, including single-photon emitters for quantum technologies, topological quantum materials, and quantum sensing and metrology: Rare-Earth Doped Thin Films for Optical Quantum Technologies (Philippe Goldner et al., 10.1002/qute.202500026): A Review article on rare earth-doped thin films—materials that are highly promising for use in on-chip photonic circuits thanks to their excellent coherence properties. The integration of rare-earth thin films into photonic platforms could potentially enable photonic quantum technologies, such as optical quantum memories, which are relevant for communications and processing. Cuprate twistronics for quantum hardware (Nicola Poccia et al., 10.1002/qute.202500203): A topical Review on the emerging field of cuprate twistronics, which involves stacking and twisting ultrathin layers of cuprate superconductors. This technique creates Moiré patterns and new electronic states, uncovering new opportunities in both applied (e.g., quantum hardware) and fundamental physics. Quantum spin Hall effects in van der Waals materials (Qiong Ma et al., 10.1002/qute.202500327): A Review of the Quantum Spin Hall (QSH) effect in two-dimensional van der Waals (vdW) materials. The QSH effect is promising for the development of low-power electronics and topological quantum computing. The article explores the main developments in the field, emerging research directions, as well as experimental challenges. Beyond kagome: p-bands in kagome metals (Alexander Tsirlin et al., 10.1002/qute.202500336): A Perspective arguing that p-bands (electron bands from non-transition metals) play a critical, often overlooked, role in the electronic instabilities, such as charge-density waves and superconductivity, observed in kagome lattice metals. High-purity single-photon emission in the telecom O-band from droplet-epitaxy InAs quantum dots integrated into a GaAs/AlGaAs planar microcavity on vicinal GaAs(111) (Battulga Munkhbat et al., 10.1002/qute.202500159): A Research article on developing a reliable source of single photons in the telecom O-band (a critical wavelength for fibre communication) using InAs quantum dots grown via droplet epitaxy. Single-photon emission from such sources could potentially be useful for building global quantum communication networks. Can Janus monolayer transition-metal dihalides be bright excitonic insulators? (Yuanchang Li et al., 10.1002/qute.202500345): This Research article explores Janus monolayers (asymmetric 2D materials) as potential candidates for bright excitonic insulators (EIs). EIs are a state of matter where electrons and holes spontaneously form excitons that condense, and bright EIs could provide a unique platform for coherent quantum optical devices. Highly sensitive magnetometer with continuous excitation Ramsey protocol by utilizing long dephasing time of millimetre-scale spin ensembles in (111) diamond (Mutsuko Hatano et al., 10.1002/qute.202500056): This Research article presents a method to significantly enhance the sensitivity of magnetometers by utilizing the long dephasing time of nitrogen-vacancy (NV) centre spin ensembles in a specific orientation of diamond. NV-diamond magnetometers are key for high-precision quantum sensing. Through this Focus Issue, we aim to highlight the major advances in quantum matter research and to offer perspectives on key directions for future research. We hope that readers will find the content of this collection both inspiring and useful.

Synaptic devices based neuromorphic computing applications in artificial intelligence

A complex interplay of different energy scales involving Coulomb repulsion, spin-orbit coupling, and Hund's coupling energy in 2D van der Waals (vdW) material produces a novel emerging physical state. For instance, ferromagnetism in vdW charge transfer insulator CrGeTe_{3} provides a promising platform to simultaneously manipulate the magnetic and electrical properties for potential device implementation using few nanometers thick materials. Here, we show a continuous tuning of magnetic and electrical properties of a CrGeTe_{3} single crystal using pressure. With application of pressure, CrGeTe_{3} transforms from a ferromagnetic insulator with Curie temperature T_{C}∼66 K at ambient condition to a correlated 2D Fermi metal with T_{C} exceeding ∼250 K. Notably, absence of an accompanying structural distortion across the insulator-metal transition (IMT) suggests that the pressure induced modification of electronic ground states is driven by electronic correlation furnishing a rare example of bandwidth-controlled IMT in a vdW material.

Nanophotonics relies on precise nanoscale structuring, yet conventional fabrication techniques remain complex and costly. Layered van der Waals (vdW) materials, with their intrinsic anisotropy and high refractive indices, offer a promising route toward simplified nanostructuring and tunable optical functionality. However, no vdW material has previously been shown to exhibit a strong photorefractive effect-a key requirement for light-based modulation. Here, we report a giant photorefractive response (Δn up to 0.3) in crystalline arsenic trisulfide (As2S3), observed at low optical intensities. In addition to refractive-index modulation, light exposure enables controlled thickness tuning of As2S3. The material exhibits a giant photoexpansion of up to 7%, depending on the illumination intensity, which may originate from light-induced generation of point defects, consistent with molecular-dynamics modeling. Building on this photoexpansion effect, we introduce a maskless nanopatterning technique based on continuous-wave laser writing, achieving ~500 nm pitch (~50,000 dpi) without the need for ultrafast lasers. The combination of high photosensitivity, anisotropy, ease of exfoliation and transfer, and optical transparency positions vdW As2S3 as a practical platform for integrated photonics, adaptive optics, reconfigurable photonic elements, and dense optical encoding.