Browse Articles

Piezovalley effect in altermagnetic Fe2WS4 and Fe2WS2Se2 monolayers

Altermagnets, which arise from the alternating crystal environment and have spontaneous spin-splitting with zero net magnetization, provide a unique opportunity for potential spintronics or valleytronics. Here, we predict two types of stable altermagnets, the Fe2WS4 monolayer and the Janus Fe2WS2Se2 monolayer, based on density functional theory calculations. It is revealed that both monolayers are found to be altermagnetic semiconductors with the valence band maximum and conduction band minimum locating around the high-symmetry point X or Y. Moreover, the altermagnetic order of Fe atom sublattices is related to M110 mirror symmetry. Under uniaxial strains, both monolayers can generate obvious valley polarization and spin polarization due to the broken of the mirror symmetry. Such piezovalley effect in Fe2WS4 and Janus Fe2WS2Se2 monolayers facilitates the design of low-power spintronic devices for information encoding.

Detection of abnormal movement in Parkinson's disease using time irreversibility and entropy

This work aims to determine how entropy and time irreversibility can help differentiate between healthy and parkinsonian movement. Acceleration signals from control subjects and patients with Parkinson's disease (PD) were analyzed using statistical tools, entropy, and time irreversibility. Results were compared with signals from three toy systems: oscillatory, random, and complex signals. Entropy values were higher in control subjects compared to Parkinson's disease patients, indicating less ordered behavior in healthy movement. Time irreversibility was found to be lower in control subjects, indicating a less dissipative system. This study provides useful insights into the differences between healthy and parkinsonian movements. Our approach shows potential to distinguish between control and PD patients in clinical practice using acceleration signals, offering a potential diagnostic tool to evaluate movement disorders such as Parkinson's disease.

Reconfigurable monolithic photonic circuit on III-nitride chip

With respect to a III-nitride monolithic photonic circuit comprising multiple quantum well (MQW) diodes, InGaN/GaN MQW transmitters/boosters convert pulse optical signals into emitted light, whereas MQW modulators/receivers/monitors transform modulated shorter-wavelength photons into electronic signals. Here, five MQW diodes are interconnected via optical waveguides on a single III-nitride monolithic photonic chip, with an operating wavelength range of 385–416 nm. By integrating functional circuits with a time-division multiplexing (TDM) scheme, the light-emitting and light-detecting functionalities of these MQW diodes can be dynamically redefined, enabling a reconfigurable optical communication architecture. Each equipotential and fully mapped node serves as a core technology for scalable on-chip optical networks, allowing the reconfigurable III-nitride photonic chip and TDM scheme to integrate additional MQW components seamlessly.

Batch-fabricated PDMS templates for the robotic transfer of 2D materials

Robotic stacking of van der Waals heterostructures has been at the verge, thanks to the convergence between artificial intelligence (AI) and two-dimensional (2D) materials research. Key ingredients to fulfill this pursuit often include algorithms to identify layer compounds on chips, hardwares to realize sophisticated operations of motion and/or rotation in a microscale, and, as importantly, highly standardized and uniform transfer stamps that are often used in picking up layered materials under a microscope. Here, we report a hot-cast-droplet batch fabrication method for polydimethylsiloxane (PDMS) templates tailored for dry transfer of 2D materials. Controlled precursor formulation, degassing, and motorized-syringe dispensing produce dome-shaped PDMS templates with ultra-smooth surfaces (root mean square roughness ∼0.3 nm at relatively low curing temperatures). By tuning the curing temperature, the reproducible and controllable apex curvature allows precisely defined contact area between the organic adhesive film and the substrate, via thermal expansion. Our results further reveal thermomechanical behaviors with different casting parameters of such PDMS domes. The capability of achieving defect-free van der Waals interfaces is further demonstrated by the fabrication of a high-quality BN/graphene/BN stack via dry transfer using the as-prepared PDMS templates. This scalable and parameterized fabrication protocol gives rise to uniform transfer stamps with ultra-smooth surface, which may be beneficial for future AI-driven robotic assembly of 2D material heterostructures.

Dual-function Sb2S3/HfO2 memristor for reservoir computing and neural network learning via decoupled short- and long-term memory

Conventional computing architectures typically rely on separate devices to achieve dynamic sensing and long-term storage, leading to low integration density, high energy consumption, and significant data movement bottlenecks. Here, a biomimetic dual-function memristor based on an Sb2S3/HfO2 heterostructure is proposed, in which synergistic regulation of ion migration and electronic transport enables the materials-assisted decoupling and coordinated integration of short-term memory (STM) and long-term memory (LTM) functions within a single device. The device successfully emulates various biological synaptic behaviors, including paired-pulse facilitation/depression, tunable excitatory postsynaptic currents (EPSCs), and highly linear long-term potentiation/depression. Subsequently, utilizing the LTM characteristics of the device, a nonvolatile synaptic array is built to implement a fully connected neural network, achieving 94.5% accuracy. Meanwhile, a physical reservoir computing system is constructed using the STM dynamics to directly encode and recognize spatiotemporal features in iris image sequences, achieving 98% accuracy. Through coordinated innovation in materials, devices, and architecture, this work advances memristors from single-function memory elements toward multifunctional, all-electrical intelligent processing units.

Charge-density wave-mediated soft phonon modes suppress the temperature dependence of lattice thermal conductivity in 2H-NbSe2

Layered NbSe2 has attracted extensive interest as a prototypical system where multiband superconductivity coexists with a charge-density wave (CDW) order. Here, using self-consistent phonon theory to incorporate anharmonic renormalization, CDW critical temperatures in the bulk and monolayer 2H-NbSe2 are calculated to be 66 and 116 K, respectively, in good agreement with reported experiments. First-principles anharmonic lattice dynamics combined with Peierls–Boltzmann transport theory reveals that strong phonon anharmonicity, arising from low-energy special soft phonon modes mediated by the CDW behavior, results in a low lattice thermal conductivity (κL) with weak temperature dependence. Strikingly, four-phonon (4ph) interactions contribute to a dramatic suppression of κL, particularly in the in-plane direction, reinforcing the critical role of strong phonon anharmonicity. These results provide a detailed microscopic understanding of CDW transition and thermal transport in CDW materials.

Coexistence of topology and superconductivity in two-dimensional anti-van't Hoff/Le Bel bonded BeC3 monolayer

Two-dimensional topological superconductors combining nontrivial band topology with robust superconductivity remain rare in light-element systems. Here, we predict a thermodynamically stable BeC3 monolayer simultaneously hosting a symmetry-protected Dirac nodal-line ring and phonon-mediated superconductivity (Tc∼12.7 K). The structure features planar hexacoordinate beryllium atoms—an “anti-van't Hoff/Le Bel” geometry that defies classical coordination principles—with dual functionality: substantial charge transfer (1.65 e/Be) stabilizes extended carbon π networks forming the Dirac nodal ring, while low-frequency out-of-plane Be vibrations (69.8% phonon contribution) drive strong electron–phonon coupling (λ=0.68) through carbon pz states at the Fermi level. Exceptional stability (up to 2400 K, cohesive energy 6.44 eV/atom) establishes BeC3 as a viable experimental target. Beyond identifying a promising topological superconductor, this work highlights the functional importance of planar hypercoordinate motifs in realizing exceptional quantum properties.

High-mobility magnetic two-dimensional electron gas with high Curie temperatures at Eu2O3/SrTiO3 interfaces

High-mobility spin-polarized two-dimensional electron gases (2DEGs) hold fundamental importance for the development of next-generation spintronic devices. In this work, we fabricate a high-quality epitaxial Eu2O3/STO (001) heterointerface, which hosts a two-dimensional electron gas exhibiting a high electron mobility of approximately 4.3 × 103 cm2 V−1 s−1 at 2 K. This interface demonstrates robust metallic conductivity, a pronounced Kondo effect, and an observable anomalous Hall effect that persists up to 100 K. Furthermore, magnetic measurements confirm the emergence of ferromagnetic order, which is primarily attributed to the combined effects of the Ti3+ magnetic moments induced by oxygen vacancies on the surface of the STO single crystal and the localized Eu2+ magnetic moments within the thin film. These collective findings support the possible formation of a spin-polarized 2DEG characterized by a high ferromagnetic ordering temperature. Our work underscores the significant potential of Eu-based oxide heterostructures as a promising platform for fundamental research of spin-polarized 2DEG.

Large critical current density Josephson <i>π</i> -junctions with PdNi barriers

We report large π-state critical current densities, Jc(π), in Nb/Pd89Ni11/Nb Josephson junctions at Pd89Ni11 thicknesses near the first π-state. We observe oscillations in the critical current with ferromagnetic barrier thickness consistent with a 0–π transition. For a junction with a 9.4 nm Pd89Ni11 barrier, we obtain Jc(π)=410 kA/cm2 at 4.2 K, exceeding values reported in prior PdNi-based studies. Magnetization measurements on continuous films, together with coercivity tests on patterned arrays, confirm that Pd89Ni11 exhibits perpendicular magnetic anisotropy, enabling zero-field operation without magnetic initialization. The combination of large Jc(π) and intrinsic anisotropy establishes Pd89Ni11 as a promising barrier material for passive π-shifters in superconducting digital logic and qubit architectures.

Cryogenic Q enhancement in 50 GHz piezoelectric resonators

Piezoelectric resonators are a critical component of many systems. Recent advances have increased the operation frequency of these resonators into the tens to hundreds of GHz; however, the performance is still limited to moderate quality factors in the low hundreds. When viewed through the lens of the frequency-quality factor product, which can illustrate frequency-scaled loss mechanisms, a perceived limit becomes apparent. To probe this limit, we characterize solidly mounted piezoelectric resonators at cryogenic temperatures (7 K). The resonators provide mechanical robustness, as well as high-frequency shear modes around 50 GHz. Both the loaded and unloaded quality factors of these modes see enhancement with the temperature reduction, suggesting the impact of temperature-dependent fundamental loss mechanisms. This provides a launching pad for further dedicated studies to examine how energy dissipation occurs in these emerging high-frequency resonators.

Achieving near-zero thermal expansion in high-entropy ceramic (Ti1/3Zr1/3Hf1/3)Sc <i>x</i> Fe1− <i>x</i> Mo2VO12

Near-zero thermal expansion materials exhibit minimal volume changes under extreme temperature fluctuations, offering significant application value in high-precision instruments, optical equipment, satellite technology, and other fields. In this study, the (Ti1/3Zr1/3Hf1/3)ScxFe1−xMo2VO12 ceramic system was designed using a high-entropy solid solution strategy. The study indicates that the high-entropy effect at the A site due to Sc3+ doping successfully suppresses the Fe2Mo3O12 phase transition temperature from 773 K to below 173 K when x ≥ 0.75, achieving a stable orthorhombic phase and near-zero thermal expansion (173–673 K) with a volumetric thermal expansion coefficient of αv = 1.2 × 10−6 K−1. Variable-temperature XRD and Raman spectroscopy reveal that the microscopic mechanism stems from the synergistic interaction between lattice anisotropy (a-axis expansion and b/c-axis contraction) and the positive anharmonicity of the 332 cm−1 vibrational mode. The material exhibits outstanding thermal stability up to 1273 K, offering a novel material solution for precision thermal management devices across a broad temperature range.

Surface nanoprocessing with unfocused beams of high-energy femtosecond lasers: A tool to produce surface characteristics libraries

We demonstrate a single-shot method for probing ultrafast laser–matter interactions using unfocused multi-terawatt femtosecond beams. The intrinsic fluence inhomogeneity of the beams is exploited to accomplish parallel, spatially encoded experiments performed under strictly identical conditions across a wide energy range in a single step, enabling systematic mapping of energy-dependent surface responses without beam scanning. As proof of the technique, the large set of simultaneously collected data points below, at, and above the threshold inherently allows for a threshold evaluation approach, different from both the diameter/depth regression analysis and the statistical method. Using copper as a test system, we quantify the fluence dependence of reflectance and morphology and identify a multi-pulse optical threshold of 0.020 J/cm2, coinciding with the onset of ablation confirmed by SEM imaging. The minimum specular reflectance observed, around 0.10%, favorably compares to the respective figures reported. Applying this parallelized surface mapping technique with high-energy laser systems featuring suitably large beam diameters thereby provides a versatile platform for exploring ultrafast laser-induced surface responses, with potential applications in material design, surface engineering, and optical damage studies.

Dynamic terahertz focal planar scanning via cascaded metasurfaces

Terahertz (THz) planar focal spot scanning is critical for imaging, sensing, and optical routing, but traditional approaches suffer from bulkiness or limited tunability. Herein, we propose a cascaded metasurface device with two mechanically rotatable dielectric layers (M1 and M2) to achieve dynamic focal scanning. The core mechanism relies on rotation-induced phase superposition: tuning angles α1 and α2 modulates the combined phase distribution, enabling continuous in-plane focal displacement. Simulations demonstrate controllable scanning under M2 rotation (α1 = 0°, α2: −75° to 75°) and opposite co-rotation (α1 = −α2: −60° to 60°), with stable focal length and efficiency. Experimental characterization via a THz near-field system confirms close agreement between simulated and measured scanning trajectories, verifying the device's predictability and reliability. This passive scheme offers simplicity, large tuning range, and broadband compatibility, avoiding external energy supplies. The proposed cascaded platform enriches THz optical manipulation tools and facilitates integration into dynamic imaging, sensing, and beam steering systems.

Diverse nanostructures of bc8 silicon mediated by controllable transition kinetics of beta-Sn silicon

Metastable polymorphs of silicon exhibit direct and narrow band gaps, offering broad application potential. The transition kinetics in the formation of metastable Si have been extensively studied, but the relationship between transition conditions and nanostructures of product phases remains unclear. Here, we report diverse nanostructures of body-centered cubic (bc8) Si formed by rapid decompression of beta-Sn Si at different rates. High-resolution transmission electron microscopy images show slow decompression results in the formation of bc8 nanocrystals with long-range order and abundant interfacial defects, including dislocation, twin, stacking fault, and internal lattice strain. In contrast, rapid decompression generates bc8 nanoclusters with a macroscopic amorphous characteristic, as evidenced by the broad diffuse halo in fast Fourier transform pattern. Statistical analysis of the size distribution shows that the grain size decreases with the increasing decompression rate, indicating a clear rate-dependent behavior. These findings provide structural evidence and mechanistic insights into the kinetically controlled formation of the metastable nanostructures for promising applications.

Bi2Ti2O7 modification-induced large strain characteristics in BNT-6BT piezoelectric ceramics

Lead-free sodium bismuth titanate and related compounds are promising piezoelectric materials. A comprehensive understanding of this series of materials remains a challenge, partly due to their structural complexity and the differences in structure and properties caused by the application of an external electric field. This study investigates the effect of doping Bi2Ti2O7 (BTO) into 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 (BNT-6BT) ceramics. The results show that the introduction of BTO increases the pseudo-cubic phase structure of BNT-6BT and breaks the ferroelectric long-range order to form more polar nanoregions. The composition induces a phase transition from the ferroelectric phase to the relaxor phase, in which oxygen vacancies may play a certain role, and the relaxor property of the ceramics is enhanced. The BNT-6BT-4wt%BTO ceramic achieves a high positive strain (0.43%) at room temperature, which is attributed to the huge strain generated during the reversible transition between the ergodic relaxor phase and the long-range ordered ferroelectric phase. Overall, BTO doping significantly modifies the properties of BNT-6BT ceramics, enabling them to exhibit reversible long-range ordered transitions under an electric field, thus providing potential for applications in precision actuators.

Nonlinear absorption transition governed by exciton and defect states in 2D (PEA)2PbI4 from visible to near-infrared

The active control of nonlinear absorption (NLA), particularly the dynamic transition between saturable absorption (SA) and reverse saturable absorption (RSA), is essential for advanced photonics such as all-optical logic gates. However, the mechanisms governing these transitions remain poorly understood, especially concerning the roles of excitonic and defect states. This work systematically investigates the broadband NLA properties of two-dimensional (2D) perovskite (PEA)2PbI4 films from 470 to 1440 nm. Abnormal RSA to SA transition is observed at 470 nm (near the continuous state absorption shoulder) under a low pump intensity of ∼20.5 GW/cm2, attributed to the competition between many-body effect induced above band edge absorption enhancement and bleaching caused by non-thermalized carriers. At 520 nm (near the exciton resonance), SA dominates due to exciton bleaching. In the 560–650 nm range, RSA dominates due to the two-photon absorption, and the coefficient dispersion can be well-described by a two-band model. Notably, a clear transition from SA to RSA appears in the near-infrared region (1240–1440 nm), where defect-state filling induces SA, followed by RSA driven by three-photon absorption. The threshold for this transition is as low as ∼57.5 GW/cm2 at 1340 nm. These findings provide a mechanistic understanding of wavelength-dependent NLA transitions in 2D perovskites, highlighting the potential of (PEA)2PbI4 for multi-band nonlinear photonic applications.

Electrical control of polarization-resolved photodetection in GeSe/MoTe2 heterostructures for optoelectronic encryption

Polarimetric optical encryption enables parallel information channels and enhanced eavesdropping prevention capabilities, improving data transmission capacity and information security. However, conventional systems rely heavily on bulky and discrete components such as polarizers and wave plates, which complicate device integration and miniaturization. To address these limitations, we demonstrate a polarization-resolved photodetector based on the heterostructure of GeSe/2H-MoTe2. Leveraging the type-II energy band arrangement and strong interface coupling between anisotropic GeSe and ambipolar 2H-MoTe2 layers, the device enables efficient carrier separation and broadband light response from visible to near-infrared regions. Under 638 nm irradiation, the device achieves self-powered operation with a responsivity of 1.98 A/W, a specific detectivity of 1.15 × 1011 Jones, and an external quantum efficiency of 387%. Moreover, the polarization ratio of the device is electrically tunable (1.47–3.17), enabling the realization of an XNOR-based optical encryption system in which polarization angles and gate voltages serve as optical data bits and electrical keys, respectively. This work not only presents an efficient strategy for enhancing polarization sensitivity and broadband self-powered detection but also establishes a route toward secure and reconfigurable optoelectronic information processing based on 2D van der Waals (vdW) heterostructures.

Magnetotransport properties of Dirac semimetal ZrTe5 in the quantum limit

We report the magnetotransport properties of zirconium pentatelluride (ZrTe5) in the Dirac semimetal phase, focusing on its magnetoresistance behavior at low temperatures. Pronounced Shubnikov–de Haas oscillations were observed in the low magnetic field regime. In the quantum limit, linear magnetoresistance and behavior consistent with a topological phase transition emerge. In-depth analyses of these phenomena and their temperature dependences suggest that both the chemical potential and the Fermi velocity may play an important role in determining the transport properties of ZrTe5 in the quantum limit. Our findings highlight the importance of band parameters in topological transport and provide insights for future studies of topological materials and the design of quantum devices.

Cloud-based collaborative CNC manufacturing framework integrating tool wear monitoring and scheduling support

Stabilization of Rydberg dissipative time crystals using a scanning Fabry–Pérot interferometer transfer lock

Stabilization of laser frequencies is critical for sensitive Rydberg measurements, including in applications such as dissipative time-crystal (DTC) dynamics, yet conventional approaches often require complex or costly hardware. We demonstrate a compact, low-cost stabilization method using a scanning Fabry–Pérot interferometer (SFPI) to transfer lock a 960 nm coupler laser to an 852 nm Cs reference laser. The lock suppresses coupler multi-MHz free-running drift and improves the Allan deviation by up to an order of magnitude, reaching &amp;lt;75 kHz at τ ∼ 66 s. Applied to DTC oscillations using a Rb 2-photon D2 transition, the second harmonic generated at 480 nm (from 960 nm lock) reduces DTC frequency drift from &amp;gt;20 kHz to a few kHz and lowers instability by more than an order of magnitude with a minimum Allan deviation of 0.2 kHz at τ &amp;lt; 10 s. These results establish SFPI-based transfer locking as a practical and accurate approach for scalable multi-laser Rydberg experiments that require long-term stability in a compact and low-cost system.