High-κ gate dielectrics are indispensable in modern transistor technology and play a pivotal role in efficient capacitive gating and suppression of leakage currents. However, the realization of industry-compatible high-κ gate dielectrics at a sub-5-Å equivalent oxide thickness (EOT) remains challenging. Here we report the realization of 1.3-nm thick hafnium oxide (HfO2) dielectrics via an industry-compatible multiple oxidation atomic layer deposition process at 200 °C. A low EOT down to 2.5 Å is demonstrated for 1.3-nm thick HfO2 dielectrics on metal gates with a low leakage current of 10-6 A/cm2 and a robust breakdown electric field of ~22.3 MV/cm. Remarkably, such low EOT high-κ/metal gates can be directly implanted into emerging two-dimensional (2D) transistors and low-power logic circuits on 8-inch wafer scale to showcase their potentials. The as-fabricated molybdenum disulfide (MoS2) transistors exhibit a large on-state current density of 260 µA/µm at source-drain bias of 0.5 V, a high on/off ratio of 108, an average subthreshold slope (SS) of 75 mV/dec, and small capacitance equivalent thickness (CET) values of 0.34 nm for gate-first transistors and 0.50 nm for gate-last transistors. Our ultra-scaled dielectrics hold significant promise for advanced semiconductor fabrication processes towards the angstrom era.

Stacking engineering provides an effective route for tailoring ferroelectric (FE) properties and electronic band structures in two-dimensional (2D) materials, thereby enabling controllable modulation of their optical responses. With the successful experimental realization of bilayer R-phase single-crystalline WS2, the fabrication of multilayer transition metal dichalcogenide heterostructures with different stacking has become feasible. However, how complex stacking sequences cooperatively regulate the intrinsic properties of such systems remains poorly understood. To address this issue, we employ first-principles calculations to systematically construct and investigate four-layer WS2 heterostructures with different H/R stacking sequences. R-stacking breaks inversion symmetry and induces out-of-plane polarization; in homostructures composed of mixed R- and H-stacking sequences, the net polarization is governed by the number and relative orientation of the R-stacked bilayers. Spin-projected band analyzes indicate that spin-valley locking is preserved across all stacking configurations and spin orientation at K valley is primarily governed by the global stacking symmetry. Layer-projected results further reveal that the relative contributions of different layers to the K-valley band-edge states depend sensitively on the stacking configuration, indicating stacking-dependent interlayer coupling effects. In addition, GW-BSE calculations capture pronounced excitonic features in the optical absorption spectra of different stacking configurations. These results establish a unified picture linking interlayer sliding, ferroelectricity, electronic structure, and optical response, highlighting stacking engineering as an effective strategy for designing reconfigurable 2D FE and valleytronic devices.

Oxygen vacancies are central to the functionality of oxides, yet they typically exist as randomly distributed point defects, limiting the ability to precisely manipulate their collective behavior. Here, we report the room-temperature formation of a long-range-ordered oxygen-vacancy superstructure in single-crystalline Aurivillius-phase Bi2WO6 thin films via a mild nitrogen-plasma treatment. This structural transformation unlocks a colossal, reversible modulation of electrical conductivity by more than nine orders of magnitude, accompanied by a striking optical transition from transparent to black. Atomic-resolution imaging and spectroscopy reveal that the vacancies selectively order within the perovskite-like tungsten oxide layers, forming a coherent defect lattice that is absent in the pristine film. Oxygen-plasma treatment removes the vacancy superstructure and restores the initial state, whereas subsequent nitrogen-plasma treatment reconstructs it, enabling repeatable room-temperature switching between distinct structural, electronic and optical states. The phenomenon is also observed in another Aurivillius member, Bi2MoO6, suggesting its generality across the Aurivillius family. These findings establish a new paradigm for atomic-scale defect engineering - using gentle plasma chemistry to construct ordered defect lattices, opening avenues for reversible property modulation in complex oxides.

Stacking engineering provides an effective route for tailoring ferroelectric (FE) properties and electronic band structures in two-dimensional (2D) materials, thereby enabling controllable modulation of their optical responses. With the successful experimental realization of bilayer R-phase single-crystalline WS2, the fabrication of multilayer transition metal dichalcogenide heterostructures with different stacking has become feasible. However, how complex stacking sequences cooperatively regulate the intrinsic properties of such systems remains poorly understood. To address this issue, we employ first-principles calculations to systematically construct and investigate four-layer WS2heterostructures with different H/R stacking sequences. R-stacking breaks inversion symmetry and induces out-of-plane polarization; in homostructures composed of mixed R- and H-stacking sequences, the net polarization is governed by the number and relative orientation of the R-stacked bilayers. Spin-projected band analyzes indicate that spin-valley locking is preserved across all stacking configurations and spin orientation atKvalley is primarily governed by the global stacking symmetry. Layer-projected results further reveal that the relative contributions of different layers to theK-valley band-edge states depend sensitively on the stacking configuration, indicating stacking-dependent interlayer coupling effects. In addition, GW-BSE calculations capture pronounced excitonic features in the optical absorption spectra of different stacking configurations. These results establish a unified picture linking interlayer sliding, ferroelectricity, electronic structure, and optical response, highlighting stacking engineering as an effective strategy for designing reconfigurable 2D FE and valleytronic devices.

Kagome metals host competing electronic orders, including charge-density-wave (CDW) order and superconductivity, shaped by intertwined lattice, electronic-correlation, and kagome-geometric effects. Here, using quantum electrodynamical density functional theory, we identify an equilibrium cavity route for reshaping this balance in the kagome metal CsV_3Sb_5. An out-of-plane polarized single-mode cavity selectively softens CDW-related phonons, counteracting pressure-induced hardening and extending the CDW instability toward higher pressures. In the high-pressure regime where the CDW instability is otherwise suppressed, cavity coupling redistributes Eliashberg spectral weight toward lower frequencies, enhances the total electron–phonon coupling (EPC), and increases the EPC-based Allen–Dynes estimate of T_c. This response originates from a charge-density redistribution induced by the out-of-plane photon mode, which modifies lattice restoring forces and drives the phonon and EPC renormalization. These results establish cavity quantum electrodynamics as a viable equilibrium route for tuning intertwined charge order, lattice dynamics, and superconductivity in kagome materials.

Twisted WSe2 hosts superconductivity, metal-insulator phase transitions, and field-controllable Fermi-liquid to non-Fermi-liquid transport properties. In this work, we use dynamical mean-field theory to provide a coherent understanding of the electronic correlations shaping the twisted WSe2 phase diagram. We find a correlated metal competing with three distinct site-polarized correlated insulators; the competition is controlled by interlayer potential difference and interaction strength. The insulators are characterized by a strong differentiation between orbitals with respect to carrier concentration and effective correlation strength. Upon doping, a strong particle-hole asymmetry emerges, resulting from a Zaanen-Sawatzky-Allen-type charge-transfer mechanism. The associated charge-transfer physics and proximity to a van Hove singularity in the correlated metal sandwiched between two site-polarized insulators naturally explains the interlayer potential-driven metal-to-insulator transition, particle-hole asymmetry in transport, and the coherence-incoherence crossover in 3.65 degrees twisted WSe2.

The quantum anomalous Hall (QAH) effect enables dissipationless transport. However, known QAH materials rarely combine ferrovalley behavior with spin-valley locking, and Néel antiferromagnets remain largely unexplored in QAH platforms. Here, we propose a spin-valley locked QAH ferrovalley state in a MnSe/Pt2HgSe3 heterostructure. Néel-ordered MnSe induces spin-polarized bands in Pt2HgSe3 via magnetic proximity, while spin-orbit coupling lifts valley degeneracy, yielding valley-dependent gaps and a sizable QAH gap of ∼40 meV at charge neutrality. Unlike conventional QAH systems, spin-valley locking is preserved in the conduction band, producing a distinct topological phase. Chemical-potential tuning drives transitions to spin-polarized anomalous valley Hall and anomalous Hall states with opposite spin-valley responses. An out-of-plane electric field reverses the Berry curvature distribution between valleys, while the Chern number and spin-valley texture are strongly coupled to the Néel vector, establishing a tunable antiferromagnetic topological-valleytronic platform.

Transparent flexible field-effect transistors (FETs) are increasingly desired for cutting-edge electronics, but the performance of flexible two-dimensional (2D) FETs still lags behind traditional rigid 2D devices. This study addresses this issue by introducing lithographically defined poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) electrodes to fabricate high-performance 2D transistors via a transfer method. Both flexible MoS₂ FET and its rigid counterpart demonstrated impressive electron mobility values of 154 ± 20.4 cm² V⁻¹ s⁻¹ and 155 ± 15.9 cm² V⁻¹ s⁻¹ , respectively. The PEDOT:PSS/MoS₂ interface interaction was meticulously characterized and computationally analyzed to elucidate the operational mechanisms. A fully transparent flexible 2D transistor with 71 % transmittance over the visible spectrum and robust FET performance under mechanical bending was also demonstrated. This work highlights the significant potential of integrating organic polymer electrodes with advanced 2D materials for novel high-performance device applications.

Twisted stacking of two-dimensional van der Waals (vdW) semiconductors creates moiré superlattices, which provides unprecedented control over quantum states and their light-matter interactions. We demonstrate that a simple twist interface between two single-crystalline bulks of hexagonal boron nitride (hBN) creates moiré quantum wells (QWs) embedded in a three-dimensional vdW structure. hBN moiré QWs strongly confine charge carriers under both optical excitation and electrical injection. Despite their indirect bandgap, they emit intense deep-ultraviolet luminescence in the extreme wavelength bands from 215 to 240 nanometers, exceeding that of state-of-the-art conventional aluminum gallium nitride (AlGaN) multiple QWs by more than an order of magnitude. Furthermore, the twist angle control allows wide tunability of luminescence energy and efficiency in moiré QWs.

Moir & eacute; quasicrystals extend the twistronics paradigm beyond crystalline order, hosting electronic properties dictated by nonperiodic symmetry. Here, we investigate the fate of the kagome lattice's defining feature, its flat band, in a moir & eacute; quasicrystal formed by a 30 degrees-twisted bilayer. Our tight-binding model reveals that the characteristic flat band of the kagome lattice undergoes a dramatic fragmentation into multiple gapped subbands, a direct consequence of interlayer coupling and the emergent 12-fold rotational symmetry. The primary gap is robust against variations in interlayer hopping strength, while the density of states (DOS) exhibits a fractal structure, with distinctive peaks and valleys originating from band hybridization and crossings. These predictions are validated by first-principles calculations for a mori & eacute; quasicrystal formed by a realistic kagome covalent organic framework, C18H12B6O6. Our work establishes twisted kagome bilayers as a promising platform for exploring correlated physics in quasiperiodic flat bands.

The recent observation of superconductivity in the vicinity of Fermi surface reconstructed insulating or metallic states has established twisted bilayers of WSe_{2} as an exciting platform to study the interplay of strong electron-electron interactions, broken symmetries, and topology. In this work, we use a first-principles, material-specific theoretical treatment that is unbiased with respect to electronic instabilities to study the emergence of electronic ordering in twisted WSe_{2} driven by gate-screened Coulomb interactions. We construct exponentially localized moiré Wannier orbitals that faithfully capture the band structure and topology of the system, project the gate-screened Coulomb interaction onto them, and use unbiased functional renormalization group techniques to resolve the momentum and orbital structure of the leading instabilities and the relevant energy scales. We find an interplay between intervalley-coherent antiferromagnetic (IVC-AFM) order and chiral, mixed-parity d/p-wave superconductivity for carrier concentrations near a displacement field and twist-angle-tunable van Hove singularity. Our microscopic approach establishes incommensurate IVC-AFM spin fluctuations as the dominant electronic mechanism driving the formation of superconductivity in θ=5.08° twisted WSe_{2} and explains key aspects of recent experiments including the asymmetric density dependence of the spin ordering with respect to the van Hove line, the single- and double-peak structure of the DOS in the ordered (hole-doped) IVC-AFM phase, the emergence of superconductivity as the density is varied across the van Hove line, and the evolution of the displacement field-density phase diagram with twist angles between 3.7°…5°. We show that the interplay of electronic correlations and nontrivial quantum geometry in tWSe_{2} manifests in orbital-selective order parameters associated to the IVC-AFM and SC states that are detectable by local spectroscopy measurements.

Because of the large-period superlattices emerging in moiré two-dimensional (2D) materials, electronic states in such systems exhibit low energy flat bands that can be used to simulate strongly correlated physics in a highly tunable setup. While many investigations have thus far focused on moiré flat bands and emergent correlated electron physics in triangular, honeycomb, and quasi-one-dimensional lattices, tunable moiré realizations of square lattices subject to strong correlations remain elusive. Here we propose a feasible scheme to construct moiré square lattice systems by twisting two or more layers of 2D materials in a rectangular lattice by 90°. We demonstrate the concept with twisted GeX/SnX (X=S, Se) moiré superlattices and calculate their electronic structures from first principles. We show that the lowest conduction flat band in these systems can be described by a square lattice Hubbard model with parameters which can be controlled by varying the choice of host materials, number of layers, and external electric fields. In particular, twisted double bilayer GeSe realizes a square lattice Hubbard model with strong frustration due to the next-nearest-neighbor hopping that could host unconventional superconductivity, in close analogy to the Hubbard model for copper-oxygen planes of cuprate high-temperature superconductors. The presented scheme uses 90° twisted 2D materials with rectangular unit cells as a promising platform for realizing the physical phenomena of square lattice Hubbard models, establishing a new route for studying its rich phase diagram of magnetism, charge order, and unconventional superconductivity in a highly tunable setting.

A topological superconductor (TSC), characterized by a topologically nontrivial bulk state and protected gapless boundary states, is a promising platform for hosting Majorana bound states. However, many TSCs are environmentally sensitive, especially when thinned to 2D atomic layers. This instability poses a major challenge for integrating TSCs into electronic devices. Addressing it requires full encapsulation and high‐quality electrical contact to the TSC layer, which have not yet been achieved. Here, a novel contact geometry is demonstrated for an encapsulated topological superconductor candidate, 2M‐WS 2 , where metal electrodes contact the exposed step‐like edges with a width of only a few nanometers. This structure yields exceptionally low contact resistance ( R C ), down to ∼ 670 Ω·µm for a single unit and ∼ 65 Ω·µm for a six‐unit 2M‐WS 2 device. Below the superconducting critical temperature ( T C ), the TSC–metal interface becomes highly transparent, as evidenced by the Andreev reflection. Furthermore, the step‐edge contact prevents contamination during fabrication, enabling unprecedentedly high‐quality devices. In encapsulated 2M‐WS 2 , twofold rotational symmetry of the critical current ( I C ) and multiple anomalous peaks are observed in the differential resistance ( dV / dI ). The anisotropic I C originates from Fermi velocity variations along in‐plane lattice directions, while the anomalous peaks suggest multigap superconductivity in 2M‐WS 2 . These results reveal the intrinsic properties of 2M‐WS 2 and offer a new path toward high‐performance TSC‐based electronics.

Engineering moiré superlattices in van der Waals heterostructures provides fundamental control over emergent electronic, structural, and optical properties allowing to affect topological and correlated phenomena. This control is achieved through imposed periodic modulation of potentials and targeted modifications of symmetries. For twisted bilayers of van der Waals materials with rectangular lattices, such as PdSe2, this work shows that one-dimensional (1D) moiré patterns emerge universally. This emergence is driven by a series of critical twist angles (CAs). We investigate the geometric origins of these unique 1D moiré patterns and develop a universal mathematical framework to predict the CAs in twisted rectangular lattices. Through a density functional theory (DFT) description of the electronic properties of twisted bilayer PdSe2, we further reveal directionally localized flat band structures, localized charge densities and strong spin-orbit coupling along the dispersive direction which points to the emergence of an effectively 1D strongly spin-orbit coupled electronic systems. This establishes twisted rectangular systems as a unique platform for engineering low-symmetry moiré patterns, low-dimensional strongly correlated and topological physics, and spatially selective quantum phases beyond the isotropic paradigms of hexagonal moiré materials.

Electrons can form an ordered solid crystal phase ascribed to the interplay between Coulomb repulsion and kinetic energy. Tuning these energy scales can drive a phase transition from electron solid to liquid, i.e., melting of Wigner crystal. Generalized Wigner crystals (GWCs) pinned to moiré superlattices have been reported by optical and scanning-probe-based methods. Using transport measurements to investigate GWCs is vital to a complete characterization, however, still poses a significant challenge due to difficulties in making reliable electrical contacts. Here, we report the electrical transport detection of GWCs at fractional fillings ν = 2/5, 1/2, 3/5, 2/3, 8/9, 10/9, and 4/3 in twisted bilayer MoSe2. We further observe that these GWCs undergo continuous quantum melting transitions to liquid phases by tuning doping density, magnetic and displacement fields, manifested by quantum critical scaling behaviors. Our findings establish twisted bilayer MoSe2 as a novel system to study strongly correlated states of matter and their quantum phase transitions.

One-dimensional (1D) moiré superlattices, generated via heterostrain, provide a unique platform for engineering electronic topology and correlated states beyond the conventional two-dimensional (2D) moiré paradigm. Unlike 2D moiré patterns, 1D moiré structures selectively include specific stacking configurations, enabling domain-level control over low-energy electronic properties. Using atomistic tight-binding simulations, we demonstrate that heterostrain applied in specific directions can eliminate metallic AA-stacking regions and induce robust band gaps. As the strain decreases, the system undergoes a sequence of insulator-metal-insulator transitions, with Dirac cone formation at a critical strain of ηc = 1.818%. Near this transition, we observe significant Fermi surface reconstructions, marked by van Hove singularities and Lifshitz transitions, and a sign reversal of both the Berry curvature and Berry curvature dipole. Our findings establish domain-selective 1D moiré engineering as a powerful approach for controlling low-energy physics, topology, and quantum phases in van der Waals heterostructures.

Two-dimensional (2D) semiconductors are promising building blocks for advanced electronic devices. However, the fabrication of high-quality 2D semiconductor wafers with engineered layers remains a challenge. Here we describe a direct wafer bonding and debonding method that can be applied to semiconductor monolayers that have been grown epitaxially on high-adhesion substrates such as sapphire. The process operates in both vacuum and a glovebox environment and requires no intermediate-layer assistance. It produces stacked 2D semiconductors with clean interfaces and wafer-scale uniformity and allows precise control of layer numbers and the interlayer twist angle. We use the approach to create different homostructures and heterostructures with 2D monolayers, including molybdenum disulfide (MoS2) and molybdenum diselenide (MoSe2). We also show that the approach can directly bond monolayer MoS2 onto high-κ dielectric substrates (HfO2 and Al2O3) while preserving its intrinsic electronic properties. A bonding and debonding strategy is used to stack epitaxially grown semiconductor monolayers into various structures with precise control of the layer number and interlayer twist angle.

Moir & eacute; materials exhibit diverse quantum properties such as superconductivity and correlated topological phases, making them ideal for studying strongly correlated systems. While moir & eacute; materials are typically formed by stacking 2D materials with interlayer interaction dominated by weak van der Waals (vdW) forces, constructing moir & eacute; covalent superlattices by fluorinating twisted bilayer graphene becomes possible. With first principles calculations, it is demonstrated that fluorination of twisted bilayer graphene (TBG) can induce covalent bonds between adjacent layers, transforming the vdW-dominated interactions. This results in enhanced modulation of the electronic structure, with abundant flat bands across the spectrum. The findings suggest that covalent moir & eacute; superlattices offer new platforms for exploring correlated quantum phenomena and moir & eacute; covalent chemistry.

The self-passivating surfaces and reduced tunneling leakage current enable the creation of ideal Schottky contacts in van der Waals (vdW) semiconductor heterojunctions. However, simultaneously achieving high rectification ratios, low reverse leakage currents, and rapid photoresponse remains challenging. Here, we present a one-dimensional (1D)/two-dimensional (2D) mixed-dimensional heterostructure photodiode to address these challenges. The significant valence band offset and minimal electron affinity difference in this structure ensure high rectification ratios and efficient charge collection. Additionally, the dimensional disparity between the 1D and 2D materials, characterized by a smaller contact area and significant thickness difference, results in low reverse leakage current and a high current on-off ratio. Moreover, it enables gate-tunable band structure transitions. Our device exhibits an exceptional rectifying ratio of 4.7 × 107 and a high on-off ratio of 5 × 107 (Vds = 2 V and, Vg = 30 V) at room temperature. Under a gate voltage of 20 V, the photodiode achieves a specific detectivity (D*) of 4.9 × 1014 Jones, a rapid response time of 14 μs, and an extended operational wavelength approaching to 1550 nm. The strategic combination of mixed-dimensional design and band engineering yields a 1D-2D p-n heterojunction photodiode with remarkable sensitivity, repeatability, and fast response, underscoring the potential of vdW semiconductors for advanced optoelectronic applications.

In flat-band systems, emergent physics can be substantially modified by the presence of another nearby electronic band. For example, a Mott˘Hubbard insulator can turn into a charge transfer insulator if other electronic states enter between the upper and lower Hubbard bands. Here, we introduce twisted double bilayer (TDB) WSe2, with twist angles near 60°, as a controllable platform in which the K-valley band can be tuned to close vicinity of the Γ-valley moiré flat band. At half-filling, correlations split the Γ-valley flat band into upper and lower Hubbard bands and a charge-transfer insulator forms between the Γ-valley upper Hubbard band and K-valley band. Using gate control, we continuously move the K-valley band across the Γ-valley Hubbard bands, and observe a tunable charge-transfer insulator gap and subsequently a continuous phase transition to a metal. The tuning of Mott˘Hubbard to charge-transfer insulator establishes valley degree of freedom as a suitable knob for transitions between exotic correlated phases. Γ and K valleys in twisted transition metal dichalcogenides have emerged as highly tunable knobs for accessing different correlated electronic states in solid-state devices. Here, the authors tune a Mott-Hubbard state to a charge-transfer insulator state in twisted double-bilayer WSe2.