Advanced Electronic Materials最新文献

Anti-ferroelectrics (AFEs) offer unique properties such as double hysteresis window, high endurance, and low latency, making them appealing for neuromorphic computing architectures. This study introduces a novel, compact, and energy-efficient neuromorphic circuit for spike-timing-dependent plasticity (STDP) synapse using AFE field-effect transistors (AFeFETs). Although AFeFETs are volatile and unsuitable for storing synaptic weights, carbon nanotube field-effect transistors (CNTFETs) are employed with multi-threshold operation to achieve nonvolatility by shifting polarization-electric field (P-E) characteristics. By leveraging the tunable hysteresis characteristics and negative differential resistance (NDR) effect of AFeCNTFETs, a nonvolatile ternary weight storage latch is demonstrated to store STDP-governed synaptic weights. Simulation results show that this synapse improves power efficiency by 30% and saves 93% of energy compared to previous works while remaining immune to power outages. This efficient neuromorphic building block paves the way for enhanced neuromorphic learning architectures.

Extreme magnetoresistance (XMR) is a phenomenon characterized by an increase in resistance by factors of 10⁴–10⁷% when a magnetic field is applied. This phenomenon is found in a number of semimetals such as WTe₂, PtSn₄, Cd₃As₂, and LaSb. The origin of XMR is still hotly debated, possibly with different materials having different (or multiple) explanations. Extreme transverse magnetoresistance of up to 8000% at 14 T and 1.8 K is measured in TiZn₁₆, a semimetal with a multitude of bands crossing the Fermi energy, akin to PtSn₄. The magnetoresistance is suppressed when the magnetic field is rotated to be parallel to the applied current, similar to PtSn₄ and PdSn₄. The resistance of TiZn₁₆ follows Kohler's rule, but displays different behavior under an applied transverse field and under a longitudinal magnetic field, suggesting distinct electrical phases. Also present are Shubnikov-de Haas and de Haas-van Alphen oscillations with a transverse magnetic field up to 43 T, showing that despite an insulator-like temperature-resistance curve, charge carriers are still present. This positions TiZn₁₆ as an interesting addition to the investigation of XMR materials as a multi-band metal with complex Fermi surface geometries.

Different from traditional ferroelectrics whose polarization stems from ionic displacements mediated by phonons, electronic ferroelectrics exhibit spontaneous polarization originating from polar electronic ordering. Such electronic mechanisms promise devices with ultrafast switching speeds, lower energy consumption, and enhanced resilience to fatigue and depolarization fields inherent in conventional ferroelectrics. While early candidates are restricted to rare oxides and organic charge-transfer salts, emerging systems—particularly 2D van der Waals moiré heterostructures—have significantly broadened this materials landscape. This review comprehensively examines ferroelectrics governed by electronic mechanisms, categorizing them according to microscopic origins, including spin correlations, charge ordering, orbital interactions, charge-transfer instabilities, and excitonic phenomena. Representative materials span multiferroics, molecular crystals, and engineered van der Waals architectures. Crucially, we evaluate whether their ferroelectricity qualifies as purely electronic—defined by the absence of ionic displacements during polarization reversal—synthesizing recent theoretical and experimental advances to establish a unified framework for this evolving paradigm.

We investigate the influence of hydrostatic pressure on the physical properties of monolayer $�{\mathrm{FeCl}}_2$ for spintronics applications. A phase transition from a ferromagnetic half-metal to a ferromagnetic semiconductor is unveiled at 4.6 GPa, accompanied by a transition from a non-polar (1T) to a polar (1H) structure. We demonstrate that hydrostatic pressure elevates the Curie temperature above room temperature (for example, 618 K at 5 GPa) and enhances the magnetic anisotropy energy (for example, 731 $��\mu �\mathrm{eV}�$ per formula unit at 5 GPa). A significant Dzyaloshinskii-Moriya interaction is present in the 1H structure (due to the broken spatial inversion symmetry) and increases with the hydrostatic pressure. Together with the observation of in-plane electric polarization (for example, 1.1 pCcm⁻¹ at 5 GPa), this positions the 1H structure as a pioneer in the class of 2D materials. Exploiting the phase transition of monolayer $�{\mathrm{FeCl}}_2$, a single-material magnetic tunnel junction is proposed and an outstanding tunneling magnetoresistance ratio is demonstrated.

The emerging nitride ferroelectrics, such as Al_1-xSc_xN promise to significantly advance our current information technology. In particular, two-terminal memristive devices are ideal candidates for artificial intelligence accelerators and in-memory computing due to their simplicity in design, non-volatility and non-destructive readout. The recent discovery of conductive domain walls in Al_1-xSc_xN is a promising enabler for such technology, offering several benefits compared to barrier height modulation- or tunneling-based devices. First, domain walls can be highly conductive and feature high read currents (required for aggressive lateral scaling and fast access times), also in non-epitaxial films without being restricted to the technologically challenging ultrathin thickness regime (10 nm). Second, nitride ferroelectrics are fully compatible with silicon and GaN technology on which the ferroelectric domain wall memory (FeDMEM) can be integrated with logic circuitry. Third, excellent scalability and temperature resistance of ferroelectric Al_1-xSc_xN were demonstrated, enabling scaled, low-latency edge computing under extreme environmental conditions. In this study, a FeDMEM device consisting of a Pt/Al_0.72Sc_0.28N/Pt capacitor grown on Si substrates is electrically characterized in-depth, revealing unique peculiarities in the memristive response. A read current density of 350 A/m² and an ON/OFF ratio of 20 is achieved, allowing for consistent storing of up to eight levels of information.

Space-time-coding metasurfaces (STCMs) enable simultaneous controls of electromagnetic wave across multiple harmonics, but designing high-performance coding sequences in real time remains challenging. Here, we propose an unsupervised physics-informed deep learning framework that can generate optimal spatiotemporal coding patterns for arbitrary single- and dual-beam requirements at each harmonic frequency. The proposed method features three key innovations: physics-informed mechanisms to enable unsupervised learning without requiring paired training data, a dedicated strategy for multi-bit metasurface configurations, and the Conflict Averse Gradient descent (CAGrad) method to coordinate the parameter optimization across harmonics in multi-task learning. Experiments on a 2-bit STCM demonstrate robust beamforming capabilities over five harmonics, achieving an average radiation difference of 1.55 dB and real-time design <0.1s. This is a 4-order-of-magnitude improvement in computational efficiency compared with the particle swarm optimization methods. This work establishes a real-time and physics-aware design paradigm for intelligent metasurfaces in the next-generation wireless systems.

2D semiconducting H-phase vanadium disulfide (VS₂) has attracted significant research interest due to its exceptional potential in electronics, optoelectronics, spintronics, and valleytronics. In this work, VS₂ thin films are synthesized via chemical vapor deposition for the application of photodetectors, revealing a tunable dual-photoconductivity effect induced by CO₂ adsorption and light-assisted desorption. CO₂ adsorption led to negative photoconductivity, achieving a remarkable responsivity of ∼2680 A/W and an ultra-high external quantum efficiency of ∼1.3 × 10⁶%. In contrast, VS₂ photodetectors free from CO₂ adsorption exhibited stable positive photoconductivity, with a maximum responsivity and external quantum efficiency of ∼0.11 A/W and ∼30.47%, respectively. First-principles calculations demonstrate that CO₂ exhibits superior adsorption and desorption capabilities on the VS₂ surface compared to other ambient gas molecules (e.g., N₂, O₂, and H₂O). This work highlights the profound influence of gas adsorption on the photoconductivity behavior of VS₂ thin films, providing critical insights into their optoelectronic properties and enabling non-destructive modulation for advanced device applications.