Jing Zhang

Nature Physics, Published online: 30 January 2023; doi:10.1038/s41567-022-01907-2

Films of the correlated oxide NdNiO3 form a metallic antiferromagnetic phase that can be identified using electrical currents, raising the prospect of applications in spintronics.

Nature, Published online: 01 February 2023; doi:10.1038/s41586-022-05612-1

We report full-colour, vertically stacked µLEDs that achieve exceptionally high array density (5,100 pixels per inch) and small size (4 µm) via a 2D material-based layer transfer technique, allowing the creation of full-colour µLED displays for augmented and virtual reality.

Nature Electronics, Published online: 31 January 2023; doi:10.1038/s41928-023-00921-3

MicroLEDs that can flex

The thickness-dependent magnetic order in 2D Cr₅Si₃ nanosheets is herein studied. The thickness-dependent topological Hall effect and its relation to the observed perpendicular magnetic anisotropy are investigated. At the same time, Cr₅Si₃ nanosheets that are compatible with the complementary metal-oxide-semiconductor technology are synthesized through the chemical vapor deposition setup. It can be used for reference for the growth of other 2D silicides.

Abstract

Antiferromagnets with noncollinear spin order are expected to exhibit unconventional electromagnetic response, such as spin Hall effects, chiral abnormal, quantum Hall effect, and topological Hall effect. Here, 2D thickness-controlled and high-quality Cr₅Si₃ nanosheets that are compatible with the complementary metal-oxide-semiconductor technology are synthesized by chemical vapor deposition method. The angular dependence of electromagnetic transport properties of Cr₅Si₃ nanosheets is investigated using a physical property measurement system, and an obvious topological Hall effect (THE) appears at a large tilted magnetic field, which results from the noncollinear magnetic structure of the Cr₅Si₃ nanosheet. The Cr₅Si₃ nanosheets exhibit distinct thickness-dependent perpendicular magnetic anisotropy (PMA), and the THE only emerges in the specific thickness range with moderate PMA. This work provides opportunities for exploring fundamental spin-related physical mechanisms of noncollinear antiferromagnet in ultrathin limit.

Nature Nanotechnology, Published online: 30 January 2023; doi:10.1038/s41565-022-01314-x

Aligning magic-angle twisted bilayer graphene to boron nitride layers introduces a gate hysteresis coexisting with its strongly correlated phases. This bistability enables electrical switching between superconducting, metallic and insulating states.

Nature Photonics, Published online: 26 January 2023; doi:10.1038/s41566-022-01144-2

A prototype integrated Ti:Sa laser is demonstrated by bonding the Ti:Sa gain medium on silicon nitride microring resonators. Lasing is demonstrated between 730 nm and 830 nm with a threshold power as low as 6.5 mW.

Nature Communications, Published online: 25 January 2023; doi:10.1038/s41467-023-36118-7

Quasi-2D halide perovskites are attracting increasing attention for light-emitting devices. Here, the authors demonstrated efficient and stable quasi-2D perovskite LEDs enabled by suppressed phase disproportionation with newly designed organic ligands.

Nature Physics, Published online: 26 January 2023; doi:10.1038/s41567-022-01903-6

The ultrafast structural dynamics in 2D perovskites are an important part of their non-equilibrium properties. Now, their visualization reveals a light-induced reduction in the antiferro-distortion initiated by the electron–hole plasma.

Nature Materials, Published online: 23 January 2023; doi:10.1038/s41563-022-01422-y

Research on two-dimensional van der Waals ferroelectrics has witnessed an explosion over the past few years. This Perspective formulates a framework by which results can be analysed, reviews recent progress, discusses mechanisms and properties for applications, and outlines challenges to be addressed.

Nature Materials, Published online: 26 January 2023; doi:10.1038/s41563-022-01438-4

Colloidal nanocrystals can form into periodic superlattices exhibiting collective vibrations from the correlated motion of the nanocrystals. This Perspective discusses such collective vibrations and their as-of-yet untapped potential applications for phononic crystals, acoustic metamaterials and optomechanical systems.

Nature, Published online: 26 January 2023; doi:10.1038/d41586-023-00143-9

Experiments on ultracold atoms reveal that disorder doesn’t stop a quantum system of interacting particles from reaching thermal equilibrium. Instead, small thermalized regions ripple like an avalanche through the whole system.

Electron Correlation

In article number 2205698, David Maximilian Janas, Andrea Droghetti, Giovanni Zamborlini, and co-workers use state-of-the art photoemission spectroscopy and theoretical methods to unravel the origin of enhanced electron correlation at the interface between iron and an oxygen adsorbate layer. Since the degree of correlation is controlled by interface charge transfer, it can be easily engineered by selecting different adsorbates. This strategy could allow the design of low-dimensional materials in yet-unexplored intermediate correlated regimes. Image credit: Mira Sophie Arndt.

A polymorphic memtransistor based on atomically thin Mo_0.91W_0.09Te₂ is achieved, where the lateral device channel can be tuned as metallic and semiconducting for diverse neuromorphic and in-memory computing.

Abstract

Modulating semiconducting channel potential has been used for electrical switching in transistors without biological plasticity operations that are critical for energy-efficient neuromorphic computing. To achieve efficient data processing, alternative transport mechanisms, such as tunneling and thermionic emission, have been introduced with 2D materials. Here, a polymorphic memtransistor based on atomically thin Mo_0.91W_0.09Te₂ is presented, where the lattice and electronic structures of the lateral device channel can be tuned as either metallic (1T′) or semiconducting (2H) phases by electrical gating. The structural and electronic phase change of the channel material, optimized in Mo_0.91W_0.09Te₂, is explored using transport and optical measurements at the device scale. Based on the phase transition, the polymorphic memtransistor demonstrates a high on/off ratio (up to 10⁵), low subthreshold swing (down to 80 mV dec⁻¹), and various memristive behaviors, which are distinguished from traditional phase-change memory, transistors, and passive memristors for diverse neuromorphic and in-memory computing.

Pellets of graphite intercalation compounds (GICs) are synthesized by the Na-catalyzed method. A_M–GICs (A_M = Li, Na, K) are formed simply by mixing A_M and graphite with Na at room temperature. A Ca-GIC (CaC₆) is formed by heating a mixture of Ca, graphite, and Na at 250 °C for only several hours.

Abstract

Graphite intercalation compounds (GICs) have a variety of functions due to their rich material variations, and thus, innovative methods for their synthesis are desired for practical applications. It is discovered that Na has a catalytic property that dramatically accelerates the formation of GICs. It is demonstrated that LiC_{6 n} (n = 1, 2), KC₈, KC_{12 n} (n = 2, 3, 4), and NaC _x are synthesized simply by mixing alkali metals and graphite powder with Na at room temperature (≈25 °C), and A_EC₆ (A_E = Ca, Sr, Ba) are synthesized by heating Na-added reagents at 250 °C only for a few hours. The NaC _x , formed by the mixing of C and Na, is understood to act as a reaction intermediate for a catalyst, thereby accelerating the formation of GICs by lowering the activation energy of intercalation. The Na-catalyzed method, which enables the rapid and mass synthesis of homogeneous GIC samples in a significantly simpler manner than conventional methods, is anticipated to stimulate research and development for GIC applications.

Se-vacancy-engineered VSe₂ is proposed to reveal the role of anion vacancies on the K⁺ storage of conversion-type anode materials. The results reveal that Se vacancies boost the first potassiation by offering additional K⁺ adsorption sites and diffusion channels in the intercalation stage and weakening bond strength in the conversion stage. In addition, Se vacancies disappear after the first potassiation.

Abstract

Anion vacancy engineering (AVE) is widely used to improve the Li-ion and Na-ion storage of conversion-type anode materials. However, AVE is still an emerging strategy in K-ion batteries, which are promising for large-scale energy storage. In addition, the role of anion vacancies on ion storage is far from clear, despite several proposed explanations. Herein, by employing VSe₂ as a model conversion-type anode material, Se vacancies are intentionally introduced (labeled as P-VSe_2−x ) to investigate their effect on K⁺ storage. The P-VSe_2−x shows excellent cyclability in half cells (143 mA h g⁻¹ at 3.0 A g⁻¹ after 1000 cycles) and high energy density in coin-type full cells (206.8 Wh kg⁻¹). By applying various electrochemical techniques, the effects of Se vacancies on the redox potentials of K-ion insertion/extraction and the K-ion diffusion in electrodes upon cycling are uncovered. In addition, the structural evolution of Se vacancies during potassiation/de-potassiation using various operando and ex characterizations is revealed. Moreover, it is demonstrated that Se vacancies can facilitate the breaking of VSe bonds upon the P-VSe_2−x conversion using theoretical calculations. This work comprehensively explains the role of anion vacancies in ion storage for developing high-performance conversion-type anode materials.

Atomically dispersed Zn(II)N₅ sites are immobilized on g-C₃N₄ nanosheets for detecting phenanthrene (PHE) by dual ratiometric fluorescence with ultrahigh sensitivity (limit of detection = 0.35 ng L⁻¹) and selectivity among typical polycyclic aromatic hydrocarbons due to favorable selective adsorption of PHE on as-constructed atomic Zn(II)N₅ sites via the ionic cation–π interactions (Zn^δ+C₂ ^δ− type).

Abstract

Ultrasensitively selective detection of trace polycyclic aromatic hydrocarbons (PAHs) like phenanthrene (PHE) is critical but remains challenging. Herein, atomically dispersed Zn sites on g-C₃N₄ nanosheets (sZn-CN) are constructed by thermal polymerization of a Zn–cyanuric acid–melamine supramolecular precursor for the fluorescence detection of PHE. A high amount (1.6 wt%) of sZn is grafted in the cave of CN with one N vacancy in the form of unique Zn(II)N₅ coordination. The optimized sZn-CN achieves a wide detection range (1 ng L⁻¹ to 5 mg L⁻¹), ultralow detection limit (0.35 ng L⁻¹, with 5-order magnitude improvement over CN), and ultrahigh selectivity toward PHE even among typical PAHs based on the built PHE-CN dual ratiometric fluorescence method. By means of in situ Fourier transform infrared spectroscopy, time-resolved absorption and fluorescence spectroscopy, and theoretical calculations, the resulting superior detection performance is attributed to the favorable selective adsorption of PHE on as-constructed atomic Zn(II)N₅ sites via the ionic cation–π interactions (Zn^δ+C₂ ^δ− type), and the fluorescence quenching is dominated by the inner filter effect (IFE) from the multilayer adsorption of PHE at low concentrations, while it is done by the protruded photogenerated electron-transfer process, as well as IFE from the monolayer adsorption of PHE at ultralow concentration.

Fe-intercalated T_d-Fe _x MoTe₂ single crystals (0 ≤ x ≤ 0.15) are grown successfully. The Fe intercalation significantly tunes the structural instability and brings about exotic electronic properties for the Weyl semimetal MoTe₂, including the first observed Kondo effect and spin-glass transition in its topologically nontrivial T_d phase at low temperature.

Abstract

Weyl semimetal T_d-MoTe₂ has recently attracted much attention due to its intriguing electronic properties and potential applications in spintronics. Here, Fe-intercalated T_d-Fe _x MoTe₂ single crystals (0 < x < 0.15 ) are grown successfully. The electrical and thermoelectric transport results consistently demonstrate that the phase transition temperature T _S is gradually suppressed with increasing x. Theoretical calculation suggests that the increased energy of the T_d phase, enhanced transition barrier, and more occupied bands in 1T′ phase is responsible for the suppression in T _S. In addition, a ρ ^α –lnT behavior induced by Kondo effect is observed with x ≥ 0.08, due to the coupling between conduction carriers and the local magnetic moments of intercalated Fe atoms. For T_d-Fe_0.15MoTe₂, a spin-glass transition occurs at ≈10 K. The calculated band structure of T_d-Fe_0.25MoTe₂ shows that two flat bands exist near the Fermi level, which are mainly contributed by the d _yz and dx2−y2${{\rm{d}}_{{x^2} - {y^2}}}$ orbitals of the Fe atoms. Finally, the electronic phase diagram of T_d-Fe _x MoTe₂ is established for the first time. This work provides a new route to control the structural instability and explore exotic electronic states for transition-metal dichalcogenides.

A novel method of fabricating high-temperature-superconductor-based van der Waals heterostructures is reported. The novel method utilizing the encapsulating heterostructure's interface overcomes detrimental effects of disorder and enables crucial improvement of the characteristics of the Josephson junction constituting the core of the proposed van der Waals material. The designed heterostructures operating at elevated temperatures holds potential for emerging quantum technologies.

Abstract

High-temperature cuprate superconductors based van der Waals (vdW) heterostructures hold high technological promise. One of the obstacles hindering their progress is the detrimental effect of disorder on the properties of the vdW-devices-based Josephson junctions (JJs). Here, a new method of fabricating twisted vdW heterostructures made of Bi₂Sr₂CuCa₂O_8+δ, crucially improving the JJ characteristics and pushing them up to those of the intrinsic JJs in bulk samples, is reported. The method combines cryogenic stacking using a solvent-free stencil mask technique and covering the interface by insulating hexagonal boron nitride crystals. Despite the high-vacuum condition down to 10⁻⁶ mbar in the evaporation chamber, the interface appears to be protected from water molecules during the in situ metal deposition only when fully encapsulated. Comparing the current–voltage curves of encapsulated and unencapsulated interfaces, it is revealed that the encapsulated interfaces’ characteristics are crucially improved, so that the corresponding JJs demonstrate high critical currents and sharpness of the superconducting transition comparable to those of the intrinsic JJs. Finally, it is shown that the encapsulated heterostructures are more stable over time.

A strong interlayer-coupled WSe₂/WSe₂ homostructure is grown by chemical vapor deposition using a heteroatom-assisted approach to overcome the stacking-free energy, showing a uniform moiré superlattice and strong interfacial coupling. The interlayer coupling can be adjusted by altering the twist angle, enabling the investigation of a variety of novel physical phenomena, which is expected to realize single-photon emission and promote the development of coherent quantum light emitters.

Abstract

Moiré superlattices in twisted van der Waals materials offer a powerful platform for exploring light–matter interactions. The periodic moiré potentials in moiré superlattices can induce strongly correlated quantum phenomena that depend on the moiré potential associated with interlayer coupling at the interface. However, moiré superlattices are primarily prepared by mechanical exfoliation and manual stacking, where the transfer methods easily cause interfacial contamination, and the preparation of high-quality bilayer 2D materials with small twist angles by growth methods remains a significant challenge. In this work, WSe₂/WSe₂ homobilayers with different twist angles by chemical vapor deposition (CVD), using a heteroatom-assisted growth technique, are synthesized. Using low-frequency Raman scattering, the uniformity of the moiré superlattices is mapped to demonstrate the strong interfacial coupling of the CVD-fabricated twist-angle homobilayers. The moiré potential depths of the CVD-grown and artificially stacked homostructures with twist angles of 1.5° are 115 and 45 meV (an increase of 155%), indicating that the depth of moiré potential can be modulated by the interfacial coupling. These results open a new avenue to study the modulation of moiré potential by strong interlayer coupling and provide a foundation for the development of twistronics.

Nature Nanotechnology, Published online: 23 January 2023; doi:10.1038/s41565-022-01312-z

In-plane anisotropic exciton-polariton propagation in SnSe enables nanoscale imaging of the in-plane ferroelectric domains

Nature Nanotechnology, Published online: 23 January 2023; doi:10.1038/s41565-022-01291-1

A neuromorphic camera can localize single fluorescent particles to below 20 nm resolution and evaluate the diffusion trajectory with millisecond temporal precision.