Jing Zhang

In this work, a novel angle multiplexed printing design method combining holographic approaches is proposed for boosting the amounts of channels in single printing element. A static 25 channel printing and a dynamic 8 channel video display are experimentally demonstrated using a spatial light modulator. Another 324 channel printing based on a gradient metasurface is illustrated through simulation.

Abstract

Multiplexed planar printings, made of single or few layer micro and nano optical platforms, are essential for high capacity display, information storage, and encryption. Although they are developed rapidly, the demonstrated channels are still limited and also lack instantaneity. Here, holograms and printings, always regarded as two independent information coding domains with totally different principles, are combined together through this proposed angle multiplexing framework, leading to multiplexed printings with hundreds of channels. Based on such approach, the authors experimentally encode, respectively, 25 gray scale printings into 25 angles and even 8 gray scale videos into 8 angles with a phase-only spatial light modulator. As a bridge between printings and holograms, this method allows to generate printings combining various holographic methods. Beneficial from this, a gradient metasurface based 324 channel printing is demonstrated which multiplexes angles, polarizations, and wavelengths simultaneously. This work paves the way to flexibly angle-dependent printing display and massively multiplexed encryption systems.

Electron spin resonance studies of a bulk antiferromagnetic semiconductor CrSBr single crystal revel: 2D magnetism, room temperature magnetic anisotropy, spin–spin correlations as well as the formation of potential topological vortex and anti-vortex pairs predicted by the BKT model. These findings together with the chemical stability and semiconducting properties, make CrSBr a promising layered magnet for future magneto- and topological electronic applications.

Abstract

2D magnets represent material systems in which magnetic order and topological phase transitions can be observed. Based on these phenomena, novel types of computing architectures and magnetoelectronic devices can be envisaged. Unlike conventional magnetic films, their magnetism is independent of the substrate and interface qualities, and 2D magnetic properties manifest even in formally bulk single crystals. However, 2D magnetism in layered materials is rarely reported often due to weak exchange interactions and magnetic anisotropy, and low magnetic transition temperatures. Here, the electron spin resonance (ESR) properties of a layered antiferromagnetic CrSBr single crystal are reported. The W-like shape angular dependence of the ESR linewidth provides a signature for room temperature spin–spin correlations and for the XY spin model. By approaching the Néel temperature the arising of competing intralayer ferromagnetic and interlayer antiferromagnetic interactions might lead to the formation of vortex and antivortex pairs. This argument is inferred by modeling the temperature dependence of the ESR linewidth with the topological Berezinskii-Kosterlitz-Thouless phase transition. These findings together with the chemical stability and semiconducting properties, make CrSBr a promising layered magnet for future magneto- and topological-electronics.

Nature Photonics, Published online: 29 August 2022; doi:10.1038/s41566-022-01060-5

Under near-infrared-light excitation, anti-Stokes-shift superfluorescence is observed near 590 nm at room temperature in a medium of lanthanide-doped upconversion nanoparticles. The spectral width and radiative decay lifetime are 2 nm and 46 ns, respectively, in the single-nanoparticle case.

Nature Communications, Published online: 29 August 2022; doi:10.1038/s41467-022-32605-5

In isotropic two dimensional systems, long range ferromagnetic order is supressed by thermal fluctuations, and it is due to magnetic anisotropy that van der Waals magnetic materials can have ferromagnetic ordering at finite temperatures. Usually this magnetic anisotropy is relatively small, but in this manuscript Zhang et al make a two dimensional van der Waals material with exceptionally large perpendicular magnetic anisotropy and ferromagnetic ordering that exits up to 350 K.

Nature Materials, Published online: 31 August 2022; doi:10.1038/s41563-022-01363-6

The success of silicon photonics is a product of two decades of innovations. This photonic platform is enabling novel research fields and novel applications ranging from remote sensing to ultrahigh-bandwidth communications. The future of silicon photonics depends on our ability to ensure scalability in bandwidth, size and power.

Nature, Published online: 31 August 2022; doi:10.1038/s41586-022-05031-2

A heterodimensional superlattice consisting of an alternating array of a two-dimensional material and a one-dimensional material shows unconventional octahedral stacking and an unexpected room-temperature anomalous Hall effect.

Nature, Published online: 31 August 2022; doi:10.1038/s41586-022-04991-9

By combining large-scale first-principles GW-BSE calculations and micro-reflection spectroscopy, the nature of the exciton resonances in WSe2/WS2 moiré superlattices is identified, highlighting non-trivial exciton states and suggesting new ways of tuning many-body physics.

A novel optical encryption scheme based on single-sized nanostructures storing multiple meta-images into different encryption levels is originally proposed and realized by Juan Deng, Bo Yan, and co-workers, as shown in article number 2200949. By introducing a camouflage strategy into Malus metasurfaces, this research ensures that even if the camouflage information is decrypted, the real information is still safe. The simple structure, high security, and scalability endow the metasurface with great potential in encryption applications and provide new insights for other related fields.

In this review, lasers integrated on silicon (Si) with different gain materials are presented. These gain materials include III–V semiconductors, germanium/germanium tin, Si with Raman effect, and rare-earth-doped thin film. In each section, the recent progress on Si-integrated lasers is presented, and the key results are discussed. The future outlook on Si-integrated lasers is also provided.

Abstract

With the emerging trend of big data and internet of things, silicon (Si) photonics technology has been developed and applied for high-bandwidth data transmission. Contributed by the advantages of Si including high refractive index, low loss, significant thermal-optical effect, and CMOS compatibility, various functional photonic devices have been demonstrated. One exception is the laser source, which is limited by the indirect bandgap of Si. Researchers have come up with different ways to make lasers on Si. This review presents the development progress of integrated laser sources on Si, with the focus on the wavelength regimes for communication. These lasers are categorized based on their gain media, including III–V semiconductor-based laser, germanium/germanium tin-based laser, Raman-based laser, and rare-earth-doped laser. The laser performance and characteristics are summarized in tables for comparison. The key results are discussed. Future perspectives on the development of integrated lasers on Si have also been provided.

The modulating of energy migration is achieved by the well-designed lanthanide dumbbell-like nanocrystals, resulting in excitation wavelength-dependent dual-mode emission. The dual-mode emission of nanocrystals is used for deep learning fluorescence imaging, where the blurred visible light information disturbed by phantom tissue can be established to a high resolution comparable to that of second near infrared window (NIR-II).

Abstract

Fluorescence bioimaging has always been a research hotspot in the field of life sciences and medicine. Although many studies focus on the promising second near infrared window (NIR-II) imaging, the NIR-II imaging with deep tissue penetration is limited by the broad emission band widths. Herein, a well-designed lanthanide doped nanocrystal is presented that can modulate the energy migration processes by controlling energy migration pathway and cerium-assisted energy transfer processes, resulting in switchable emission modes of visible and NIR-II that dependent by the excitation wavelengths. Subsequently, the multimode emissions of dumbbell-like nanocrystals are cooperated with deep learning, where the advantages of narrow emission peak of visible fluorescence and deep tissue penetration of NIR-II fluorescence are combined to offer a unique deep learning fluorescence bioimaging. By this new imaging method, fluorescence signals can be obtained with narrow emission peak and high signal-to-noise ratio after penetrating phantom tissue. This study brings a powerful idea for cutting-edge applications of intelligent optical materials, such as in vivo information security.

A facial dopant-induced self-assembling strategy is reported to fabricate the ultracompact grain-to-grain nanocomposite (LaFeO₃/ZnFe₂O₄/La₂O₃) with an exceptionally high piezoelectric coefficient (d₃₃) up to 826 pm V^-1 and enhanced piezo-phototronic effect. As a result, a superior oxygen activation for the generation of H₂O₂ and reactive oxygen species (in open air and pure water) is achieved via piezo-photocatalysis.

Abstract

Piezoelectric polarization portrays a promising technology to regulate the photogenerated charge carrier separation and transfer behaviors, and the design of multifunctional catalysts with piezo-phototronic effect is a key step. One strategy is to prepare a composite catalyst combining the ideal properties from each individual component. Herein, a facial dopant-induced self-assembling strategy is reported to fabricate an ultracompact nanocomposite (LaFeO₃/ZnFe₂O₄/La₂O₃) with enhanced efficiency for piezo-photocatalysis. The composite is synthesized at 800 °C from the one-pot method, thus the self-constructed interface is created during multi-phase formation, providing the intimate grain-to-grain contact between the semiconductive LaFeO₃ and piezoelectric ZnFe₂O₄/La₂O₃ phases. In such a composite, a synergistic effect for oxygen activation is realized via the effective manipulation of the photogenerated charge carrier separation and spatial transportation through the vibration-created piezopotential. A high piezoelectric coefficient (d₃₃) up to 826 pm V⁻¹ and a superior H₂O₂ yield of 403 µmol g⁻¹ h⁻¹ (in open air and pure water) are achieved on the optimized composite, outperforming most of the reported lead-free piezo-photocatalyst. The ultracompact composite is very robust without any decay in H₂O₂-delivering capability after many cyclic tests. This study provides a universal strategy for the rational design of high-performance piezo-photocatalysts.

A novel wrinkled photonic elastomer with a spider hair-like structure is used for visual strain sensing. Based on the comprehensive control of the wrinkle and lattice structure, the elastomer's vivid color can realize angle-independence, delayed discoloration, and invisible-visible conversion. The wrinkled photonic structure has superior stability, which can the maintain wrinkle structure and stable structural color performance after 1000 strain cycles.

Abstract

Color is an excellent carrier of information between organisms. Photonic elastomers that convert abstract mechanical information into intuitive color information have shown great potential in various application fields. However, angular correlation of structural colors and monotonous color conversion mode affect the accuracy of material information reading and the applicability in diverse application scenarios. Here, inspired by a kind of bright blue spider- Poecilotheria metallica, a new wrinkled photonic elastomer structure is reported. Through wrinkling stretchable 1D photonic crystals (1DPCs), photonic elastomers with both one-directional and omni-directional angle-independent brilliant structural colors are realized. It is worth noting that with the hybrid 1DPC and polydimethylsiloxane substrate support, the wrinkled photonic structure and structural color remain stable after 1000 strain cycles, and mechanochromic sensitivity can reach 3.25 nm/%, indicating strong structural stability and sensitive deformation performance under stress. More importantly, by comprehensively manipulating micro-wrinkle structure and lattice spacing of the photonic films, the structural color can achieve delayed discoloration and invisible-visible reversible switching performance only through a single strain direction. The proposed wrinkled photonic elastomers have a broad application value in the fields of visual strain sensing, wearable devices, and information encryption. Furthermore, it provides a new strategy for color regulation of photonic materials.

Intrinsic (trap-free) field-effect transistors based on epitaxial single-crystalline CsPbBr₃ perovskite films are reported. Extensive structural, electrical, and gated Hall-effect characterization confirms outstanding quality of the material and a nearly ideal transistor behavior. Hole mobility of 30 cm² V⁻¹ s⁻¹ at room temperature, monotonically increasing on cooling to 250 cm² V⁻¹ s⁻¹ at 50 K, is measured in these transistors.

Abstract

The first experimental realization of the intrinsic (not dominated by defects) charge conduction regime in lead-halide perovskite field-effect transistors (FETs) is reported. The advance is enabled by: i) a new vapor-phase epitaxy technique that results in large-area single-crystalline cesium lead bromide (CsPbBr₃) films with excellent structural and surface properties, including atomically flat surface morphology, essentially free from defects and traps at the level relevant to device operation; ii) an extensive materials analysis of these films using a variety of thin-film and surface probes certifying the chemical and structural quality of the material; and iii) the fabrication of nearly ideal (trap-free) FETs with characteristics superior to any reported to date. These devices allow the investigation of the intrinsic FET and (gated) Hall-effect carrier mobilities as functions of temperature. The intrinsic mobility is found to increase on cooling from ≈30 cm² V⁻¹ s⁻¹ at room temperature to ≈250 cm² V⁻¹ s⁻¹ at 50 K, revealing a band transport limited by phonon scattering. Establishing the intrinsic (phonon-limited) mobility provides a solid test for theoretical descriptions of carrier transport in perovskites, reveals basic limits to the technology, and points to a path for future high-performance perovskite electronic devices.

VO₂ manifests a remarkable metal–insulator transition that affords the nonlinear, dynamical response needed to emulate the function of biological neurons and synapses. Neuromorphic function is tunable through site-selective modification, stress, tuning of interfaces, and modification of external circuit elements. Strategies for modulating transformation characteristics are reviewed and inverse design approaches across decades of length and time scales are outlined.

Abstract

Future-generation neuromorphic computing seeks to overcome the limitations of von Neumann architectures by colocating logic and memory functions, thereby emulating the function of neurons and synapses in the human brain. Despite remarkable demonstrations of high-fidelity neuronal emulation, the predictive design of neuromorphic circuits starting from knowledge of material transformations remains challenging. VO₂ is an attractive candidate since it manifests a near-room-temperature, discontinuous, and hysteretic metal–insulator transition. The transition provides a nonlinear dynamical response to input signals, as needed to construct neuronal circuit elements. Strategies for tuning the transformation characteristics of VO₂ based on modification of material properties, interfacial structure, and field couplings, are discussed. Dynamical modulation of transformation characteristics through in situ processing is discussed as a means of imbuing synaptic function. Mechanistic understanding of site-selective modification; external, epitaxial, and chemical strain; defect dynamics; and interfacial field coupling in modifying local atomistic structure, the implications therein for electronic structure, and ultimately, the tuning of transformation characteristics, is emphasized. Opportunities are highlighted for inverse design and for using design principles related to thermodynamics and kinetics of electronic transitions learned from VO₂ to inform the design of new Mott materials, as well as to go beyond energy-efficient computation to manifest intelligence.

By maneuvering the supramolecular dynamics in a molecular memristor, a wide variation of functionalities starting from diode and passing between nonvolatile and volatile, unipolar and bipolar memristors with sharp and gradual transitions within a single circuit element is captured. A mathematical design space evolves thereof that can enable almost all possible characteristic variations, desirable in neuromorphic devices.

Abstract

Electronic transitions in molecular-circuit elements hinge on complex interactions between molecules and ions, offering a multidimensional parameter space to embed, access, and optimize material functionalities for target-specific applications. This opportunity is not cultivated in molecular memristors because their low-temperature charge transport, which is a route to decipher molecular many-body interactions, is unexplored. To address this, robust, temperature-resilient molecular memristors based on a Ru complex of an azo aromatic ligand are designed, and current–voltage sweep measurements from room temperature down to 2 K with different cooling protocols are performed. By freezing out or activating different components of supramolecular dynamics, the local Coulombic interactions between the molecules and counterions that affect the electronic transport can be controlled. Operating conditions are designed where functionalities spanning bipolar, unipolar, nonvolatile, and volatile memristors with sharp as well as gradual analog transitions are captured within a single device. A mathematical design space evolves, thereof comprising 36 tuneable parameters in which all possible steady-state functional variations in a memristor characteristic can be attainable. This enables a deterministic design route to engineer neuromorphic devices with unprecedented control over the transformation characteristics governing their functional flexibility and tunability.

Epitaxially grown vertical layered heterostructures (VLHs) of mixed 2D layered materials are often thought to align without angular misorientation. However, it is shown that high-mismatch VLHs show discrete and sometimes non-zero twist angles dependent on their natural lattice mismatch value. This opens a pathway for scalable Moire VLH systems.

Abstract

Artificially introduced small twist angles at the interfaces of vertical layered heterostructures (VLHs) have allowed deterministic tuning of electronic and optical properties such as strongly correlated electronic phases and Moiré excitons. But creating a Moiré twist in van der Waals (vdWs) systems by manual stacking is challenging in reproducibility, uniformity, and accuracy of the twist angle, which hinders future studies. Here, it is demonstrated that contrary to the commonly believed 0°-orientation in vdWs epitaxy, these VLHs show small twist angles controlled by the low-order commensurate phase with low energy and local atomic relaxation. A commensurate multilevel map is proposed to predict possible orientations. Remarkably, high-mismatch VLHs show discrete and sometimes non-zero twist angles dependent on their natural mismatch value. Such framework is experimentally confirmed in five epitaxially grown VLHs under high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), and can provide significant insights for large-scale engineering of twist angle in VLHs.

The magic-angle twisted trilayer graphene (MATTG) hosts robust superconductivity with unique properties, including the Pauli-limit violating and re-entrant behaviors. A systematic investigation combining nanometer-scale spatially resolved angle-resolved photoemission spectroscopy and scanning tunneling microscopy/spectroscopy on MATTG revealing the coexistence of the Dirac band and the moiré flat band serves as a stepstone for further understanding of the unconventional superconductivity in MATTG.

Abstract

Moiré superlattices that consist of two or more layers of 2D materials stacked together with a small twist angle have emerged as a tunable platform to realize various correlated and topological phases, such as Mott insulators, unconventional superconductivity, and quantum anomalous Hall effect. Recently, magic-angle twisted trilayer graphene (MATTG) has shown both robust superconductivity similar to magic-angle twisted bilayer graphene and other unique properties, including the Pauli-limit violating and re-entrant superconductivity. These rich properties are deeply rooted in its electronic structure under the influence of distinct moiré potential and mirror symmetry. Here, combining nanometer-scale spatially resolved angle-resolved photoemission spectroscopy and scanning tunneling microscopy/spectroscopy, the as-yet unexplored band structure of MATTG near charge neutrality is systematically measured. These measurements reveal the coexistence of the distinct dispersive Dirac band with the emergent moiré flat band, showing nice agreement with the theoretical calculations. These results serve as a stepstone for further understanding of the unconventional superconductivity in MATTG.

Advanced Materials, Volume 34, Issue 35, September 1, 2022.

Nature Photonics, Published online: 25 August 2022; doi:10.1038/s41566-022-01058-z

Researchers demonstrated a gate-tunable graphene photodetector with a bandwidth of up to 220 GHz. This was achieved by suppressing the ‘RC’ time constant using a resistive zinc oxide top gate.

Nature Communications, Published online: 25 August 2022; doi:10.1038/s41467-022-32534-3

Here, the authors investigate excitonic transitions in mono- and multi-layer WSe2 and MoSe2 by time-resolved Faraday ellipticity (TRFE) with in-plane magnetic fields, and attribute the oscillatory TRFE signal in the multilayer samples to pseudospin quantum beats of excitons, a manifestation of spin- and pseudospin layer locking.

Nature Materials, Published online: 24 August 2022; doi:10.1038/s41563-022-01331-0

Epitaxial heterostructures of multi-dimensional halide perovskites are demonstrated by ligand-assisted welding, providing a platform for realizing hybrid systems with unique combined properties.

Deep-learning tools can help to construct historical, modern-day, and future food webs

Nature, Published online: 24 August 2022; doi:10.1038/s41586-022-05004-5

A mechanical integrated circuit material based on Boolean mathematics and reconfigurable electrical circuits is created to demonstrate scalable information processing in synthetic, engineered soft matter.

Nature, Published online: 25 August 2022; doi:10.1038/d41586-022-02322-6

Interaction between glass spheres suspended in a vacuum might one day lead to advances in quantum computing.

Ge₄Se₉, a new insulating 2D-layered material, is synthesized using metal–organic chemical vapor deposition at 240 °C with low-reactive precursors. The 2D-layered Ge₄Se₉ forms a low band offset with MoS₂, exhibiting a large memory window with linear gate-tunability. As an artificial synapse, the MoS₂/Ge₄Se₉ heterostructure exhibits synaptic updates with low non-linearity of 0.26 and low energy consumption of 15 fJ.

Abstract

Van der Waals (vdW) heterostructures have drawn much interest over the last decade owing to their absence of dangling bonds and their intriguing low-dimensional properties. The emergence of 2D materials has enabled the achievement of significant progress in both the discovery of physical phenomena and the realization of superior devices. In this work, the group IV metal chalcogenide 2D-layered Ge₄Se₉ is introduced as a new selection of insulating vdW material. 2D-layered Ge₄Se₉ is synthesized with a rectangular shape using the metalcorganic chemical vapor deposition system using a liquid germanium precursor at 240 °C. By stacking the Ge₄Se₉ and MoS₂, vdW heterostructure devices are fabricated with a giant memory window of 129 V by sweeping back gate range of ±80 V. The gate-independent decay time reveals that the large hysteresis is induced by the interfacial charge transfer, which originates from the low band offset. Moreover, repeatable conductance changes are observed over the 2250 pulses with low non-linearity values of 0.26 and 0.95 for potentiation and depression curves, respectively. The energy consumption of the MoS₂/Ge₄Se₉ device is about 15 fJ for operating energy and the learning accuracy of image classification reaches 88.3%, which further proves the great potential of artificial synapses.

The magneto-transport properties of 2D CrSBr vertical van der Waals heterostructures are inspected, revealing a spontaneous spin alignment along the b-axis together with spin-reorientation and field-induced phases. In multilayers, a spin-valve behavior is observed with large negative magnetoresistance. This makes CrSBr of high interest not only as a new 2D magnetic model but also as a potential spintronic component.

Abstract

2D magnetic materials offer unprecedented opportunities for fundamental and applied research in spintronics and magnonics. Beyond the pioneering studies on 2D CrI₃ and Cr₂Ge₂Te₆, the field has expanded to 2D antiferromagnets exhibiting different spin anisotropies and textures. Of particular interest is the layered metamagnet CrSBr, a relatively air-stable semiconductor formed by antiferromagnetically-coupled ferromagnetic layers (T _c∼150 K) that can be exfoliated down to the single-layer. It presents a complex magnetic behavior with a dynamic magnetic crossover, exhibiting a low-temperature hidden-order below T*∼40 K. Here, the magneto-transport properties of CrSBr vertical heterostructures in the 2D limit are inspected. The results demonstrate the marked low-dimensional character of the ferromagnetic monolayer, with short-range correlations above T _c and an Ising-type in-plane anisotropy, being the spins spontaneously aligned along the easy axis b below T _c. By applying moderate magnetic fields along a and c axes, a spin-reorientation occurs, leading to a magnetoresistance enhancement below T*. In multilayers, a spin-valve behavior is observed, with negative magnetoresistance strongly enhanced along the three directions below T*. These results show that CrSBr monolayer/bilayer provides an ideal platform for studying and controlling field-induced phenomena in two-dimensions, offering new insights regarding 2D magnets and their integration into vertical spintronic devices.

Advanced Materials, Volume 34, Issue 34, August 25, 2022.

The experimental observation of Leggett collective modes in the superconducting state of a 2D transition metal dichalcogenide (TMD) is reported. Leggett modes have been rarely seen in nature and represent the first type of collective modes observed in 2D TMD superconductors, which highlights the rather unconventional superconducting properties of this family of materials in the single-layer limit.

Abstract

In certain unconventional superconductors with sizable electronic correlations, the availability of closely competing pairing channels leads to characteristic soft collective fluctuations of the order parameters, which leave fingerprints in many observables and allow the phase competition to be scrutinized. Superconducting layered materials, where electron–electron interactions are enhanced with decreasing thickness, are promising candidates to display these correlation effects. In this work, the existence of a soft collective mode in single-layer NbSe₂, observed as a characteristic resonance excitation in high-resolution tunneling spectra is reported. This resonance is observed along with higher harmonics, its frequency Ω/2Δ is anticorrelated with the local superconducting gap Δ, and its amplitude gradually vanishes by increasing the temperature and upon applying a magnetic field up to the critical values (T _C and H _C2), which sets an unambiguous link to the superconducting state. Aided by a microscopic model that captures the main experimental observations, this resonance is interpreted as a collective Leggett mode that represents the fluctuation toward a proximate f-wave triplet state, due to subleading attraction in the triplet channel. These findings demonstrate the fundamental role of correlations in superconducting 2D transition metal dichalcogenides, opening a path toward unconventional superconductivity in simple, scalable, and transferable 2D superconductors.