Jing Zhang

Nature Communications, Published online: 04 April 2023; doi:10.1038/s41467-023-37125-4

Spin-triplet exciton condensation has been predicted in perovskite cobaltites in high magnetic fields. Here, the authors report the magnetic phase diagram of LaCoO3 from magnetostriction measurements in ultrahigh magnetic fields and reveal new high-field phases with signatures of the exciton condensate.

Nature Physics, Published online: 06 April 2023; doi:10.1038/s41567-023-01991-y

Levitated nanoparticles can now be cooled to the motional ground state in two dimensions. This advance could enable a new generation of macroscopic quantum experiments.

Layered van der Waals materials have risen as a powerful platform to engineer artificial competing states of matter. Here we show the emergence of multiferroic order in twisted chromium trihalide bilayers, an order fully driven by the moiré pattern and absent in aligned multilayers. Using a combination of spin models and ab initio calculations, we show that a spin texture is generated in the moiré supercell of the twisted system as a consequence of the competition between stacking-dependent interlayer magnetic exchange and magnetic anisotropy. An electric polarization arises associated with such a non-collinear magnetic state due to the spin–orbit coupling, leading to the emergence of a local ferroelectric order following the moiré. Among the stochiometric trihalides, our results show that twisted CrBr3 bilayers give rise to the strongest multiferroic order. We further show the emergence of a strong magnetoelectric coupling, which allows the electric generation and control of magnetic skyrmions. Our results put forward twisted chromium trihalide bilayers, and in particular CrBr3 bilayers, as a powerful platform to engineer artificial multiferroic materials and electrically tunable topological magnetic textures.

Transition metal dichalcogenides have been the subject of numerous studies addressing technological applications and fundamental issues. Single-layer PtSe2 is a semiconductor with a trivial bandgap, in contrast, its counterpart with of Se atoms substituted by Hg, Pt2HgSe3 (jacutingaite, a naturally occurring mineral) is a 2D topological insulator with a large bandgap. Based on ab-initio calculations, we investigate the energetic stability, and the topological transition in Pt(HgxSe)2 as a function of alloy concentration, and the distribution of Hg atoms embedded in the PtSe2 host. Our findings reveal the dependence of the topological phase with respect to the alloy concentration and robustness with respect to the distribution of Hg. Through a combination of our ab-initio results and a defect wave function percolation model, we estimate the random alloy concentration threshold for the topological transition to be only . Our results expand the possible search for non-trivial topological phases in random alloy systems.

Nature, Published online: 05 April 2023; doi:10.1038/s41586-023-05848-5

A single-element ferroelectric state is observed in a black phosphorus-like bismuth layer, in which the ordered charge transfer and the regular atom distortion between sublattices happen simultaneously and ferroelectric switching is further visualized experimentally.

Nature, Published online: 05 April 2023; doi:10.1038/s41586-023-05815-0

By creating nanosized grains and defects in lanthanum trihydride, its electronic conductivity can be suppressed, transforming it into a superionic conductor at −40 °C with a record high H− conductivity.

Nature Communications, Published online: 01 April 2023; doi:10.1038/s41467-023-37500-1

The optical quality of large-area transition metal dichalcogenide (TMD) monolayers is usually limited by surface defects and inhomogeneities. Here, the authors report a method based on 1-dodecanol encapsulation to improve the optical properties of TMD monolayers over mm-scale, enabling the fabrication of an array of polariton photonic crystal cavities.

Nature Communications, Published online: 01 April 2023; doi:10.1038/s41467-023-37505-w

Recently there has been interest in exploring the coupling between magnons for use in information processing, however, this is hampered by the fact that such coupling is forbidden due to the different parity of the acoustic and optical magnons. Here, Comstock et al show that the interlayer Dzyaloshinskii–Moriya-Interaction in a layered hybrid antiferromagnet can allow for strong coupling between the acoustic and optical magnons, offering a pathway for magnon coherent information processing.

By immobilizing on activated carbon, a widespread food additive, riboflavin (anode) and quercetin (cathode), common food ingredients and dietary supplements, a rechargeable edible battery is demonstrated. An acqueous electrolyte, a nori algae separator and a beeswax encapsulation complete the cell, which can operate at 0.65 V.

Abstract

Edible electronics is a growing field that aims to produce digestible devices using only food ingredients and additives, thus addressing many of the shortcomings of ingestible electronic devices. Edible electronic devices will have major implications for gastrointestinal tract monitoring, therapeutics, as well as rapid food quality monitoring. Recent research has demonstrated the feasibility of edible circuits and sensors, but to realize fully edible electronic devices edible power sources are required, of which there have been very few examples. Drawing inspiration from living organisms, which use redox cofactors to power biochemical machines, a rechargeable edible battery formed from materials eaten in everyday life is developed. The battery is realized by immobilizing riboflavin and quercetin, common food ingredients and dietary supplements, on activated carbon, a widespread food additive. Riboflavin is used as the anode, while quercetin is used as the cathode. By encapsulating the electrodes in beeswax, a fully edible battery is fabricated capable of supplying power to small electronic devices. The proof-of-concept battery cell operated at 0.65 V, sustaining a current of 48 µA for 12 min. The presented proof-of-concept will open the doors to new edible electronic applications, enabling safer and easier medical diagnostics, treatments, and unexplored ways to monitor food quality.

A strain modulation strategy to expanse the surface lattice of the GaN epilayer and thus enhancing the indium incorporation in InGaN multiple quantum wells is proposed. High-efficiency InGaN red mini-light emitting diode (LED) chip with external quantum efficiency value up to 7.4% and full-color nitride mini-LED display are demonstrated. The results provide a convenient solution to accelerate the development of full-color mini/micro-LED displays.

Abstract

InGaN red light emitting diode (LED) is one of the crucial bottlenecks that must be broken through to realize high-resolution full-color mini/micro-LED displays. The efficiency of InGaN LEDs drops rapidly as the emission spectra go from blue/green to red range due to the poor quality of high-indium-content InGaN materials. Here, high-performance InGaN red LEDs on sapphire grown by metal–organic chemical vapor deposition through strain modulation are reported. A composite buffer layer is proposed to increase the surface lattice constant of GaN and hence successfully enhances the indium incorporation efficiency of the following InGaN active layers. Consequently, a high-efficiency InGaN red mini-LED chip (mesa area: 100 × 200 µm²) with a peak wavelength of 629 nm and an external quantum efficiency of 7.4% is realized. Finally, a full-color nitride mini-LED display panel with 74.1% coverage of Rec.2020 color gamut by using the InGaN red mini-LED chips is fabricated. The study signifies the great potentials of full-nitrides high-resolution full-color mini/micro-LED displays.

2D violet phosphorus (VP) nanosheets are utilized as self-powered photoelectrochemical-type photodetector. The results indicate that VP nanosheets achieve preferable photo-response activities from ultraviolet to visible region along with good chemical and environmental stability.

Abstract

Violet phosphorus (VP) is a stable layered van der Waals phosphorus allotrope with unique electronic and optoelectronic properties. In this study, 2D VP nanosheets (NSs) are prepared by liquid phase exfoliation (LPE) method under ambient conditions. The prepared VP NSs are characterized and utilized for photoelectrochemical (PEC)-type photodetector (PD). The systematic PEC measurements reveal that the as-prepared VP-based PD shows tunable photo-response activities from ultraviolet to visible region. A current density of 0.52 µA cm⁻², a photo-responsivity of 31.70 µA W⁻¹, and a detectivity of 7.92 × 10¹⁰ Jones can be obtained in 1.0 m KOH under 350 nm irradiation at 0 V, revealing the good self-powered capability of VP-based PD. Furthermore, the cycle and time stability tests exhibit the good chemical and environmental stability of the as-prepared PD via processing 10 000 s on/off switching and placing after one month. It is expected that this work can offer an understanding of a PEC-type VP NSs-based PD, and highlight the further promising applications of 2D VP NSs for other optoelectronic devices.

A direct handle on the pristine out-of-plane polarization of prototypical ferroelectric Pb(Zr_0.2Ti_0.8)O₃ PZT thin films is shown by tailoring the epitaxial growth environment. When triggered by the substrate temperature and/or the oxygen partial pressure, the changing defect chemistry near the film surface favors a downward-oriented polarization, independent of the polarization preferred by the original electrostatic boundary conditions.

Abstract

The integration of thin-film ferroelectrics with reliable properties into oxide electronics requires accomplishing deterministic polarization states. Since ferroelectricity emerges during thin-film synthesis already, it is essential to elucidate how the interplay of different growth parameters affects the polarization. Here, the polarization of fully strained Pb(Zr_0.2Ti_0.8)O₃ (PZT) films is accessed in situ, during epitaxial growth. Surprisingly, it is found that the orientation of the out-of-plane polarization during growth may differ from the one after growth completion and it strongly depends on the substrate temperature and the oxygen partial pressure. Increasing the growth temperature and/or the oxygen partial pressure favors a uniform downward-oriented polarization, independent of the direction of polarization during growth. Specifically, for films with an emerging upward-oriented polarization, a polarization reversal and a downward-oriented polarization after cool-down is observed. The in situ measurements obtained by optical second harmonic generation (SHG) in conjunction with ex situ piezoresponse force microscopy (PFM) and X-ray diffraction (XRD) measurements point to the temperature- and pressure-dependent formation of a charged Pb defect gradient toward the film surface as the responsible mechanism for the polarization reorientation.

Through cryogenic real-space imaging, exfoliated flakes of the ferromagnetic semiconductor Cr₂Ge₂Te₆ are shown to support a rich phase diagram of magnetic domain structures, including both topologically-protected and topologically-trivial lattices of magnetic bubbles. The type and chirality of these bubble can be controlled by topographic variations in the flake, and magnetoelastic coupling is shown to align and organize both bubble lattices and stripe domains.

Abstract

Ferromagnetic van der Waals (vdW) materials are of large current interest for the fundamental study of low-dimensional magnetism and for potential applications in multilayer heterostructures. Cr₂Ge₂Te₆ (CGT) is particularly exciting because it is a ferromagnetic semiconductor with tunable electronic and magnetic properties. Controlling the magnetic domain structure of CGT is a requirement for understanding its novel interface physics and for tuning behavior for potential devices. Herein, cryo-Lorentz transmission electron microscopy is performed in the temperature range of 12–50K to directly image the magnetic domain structures in CGT. A rich phase diagram of domain structures including stripe domains, magnetic bubble lattices of mixed-chirality, and topologically-protected lattices of homochiral magnetic bubbles is observed. The types and chiralities of the bubbles can be controlled by topographical changes in the CGT flakes. Additionally, it is observed that in-plane strain and magnetoelastic coupling can align and organize both bubble lattices and stripe domains. This study provides insights into creating and controlling complex magnetic domain structures for integration into multilayer heterostructures and for future studies of 2D magnetism.

The co-doped Sm³⁺ acts as electron trap in the afterglow process demonstrated by the characteristic emission and the X-ray absorption near-edge structure (XANES) spectra of Sm²⁺ before and after excitation in BaZrSi₃O₉:Eu²⁺, Sm³⁺, which is also present in samples co-doped with other Ln³⁺. Thus, the type of carriers and traps in this afterglow mechanism is clarified.

Abstract

BaZrSi₃O₉:Eu²⁺, Sm³⁺ (Em:525 nm) is prepared. The role played by the trivalent co-doping ion Sm³⁺ in the afterglow and the type of trap are clarified. BaZrSi₃O₉:Eu²⁺, Sm³⁺ is found to produce Sm²⁺ during the excitation by X-ray absorption near-edge structure (XANES), etc., and it is thus proved that Sm³⁺ exists as an electron trap in the afterglow process. In the field of persistent phosphors activated by Eu²⁺ and Re³⁺ such as Sm³⁺ or Dy³⁺ having been widely utilized as emergency guide lights, clock faces, etc. for > 25 years, for the first time it is successfully observed that after excitation Re²⁺ is formed, transferring its electron to 5d band of Eu²⁺, returning to Re³⁺ by itself, where the decrease in Sm²⁺ coincides with the increase in Sm³⁺, and the two decay time τ₁ and τ₂ of PL (⁵D₀→⁷F₀) of Sm²⁺ coincides with the two evolution time of PL (5d→4f) of Eu²⁺. The behavior of electron transfer from Sm²⁺ to Eu²⁺ as a key of afterglow is detected. The detailed afterglow mechanism is proposed by analysis of thermoluminescence and defect reaction, which is very important for the in-depth investigation of the long afterglow material and the further improvement of the mechanism.

Growth mechanism of thermally evaporated γ-CsPbI₃ is elucidated in aspect of perovskite formation and stabilization. The kinetic energies of evaporated molecules and the substrate thermo synergistically provide the formation energy. Also, the small grain size reduces the Gibbs free energy to make it stabilize. By adjusting the grain size, the optimal efficiency is 12.75% without any additives or high temperature.

Abstract

Cesium lead triiodide (CsPbI₃) inorganic perovskite possesses excellent thermal stability and matched bandgap for silicon-based tandem photovoltaics. The solution method with high-temperature annealing process for CsPbI₃ film preparation creates challenges to scalable application and conformal growth on the textured silicon. Although additives can decrease the annealing temperature, it will introduce undesired organic components and increase material cost. Thermal co-evaporation for CsPbI₃ has intrinsic advantages to overcome these issues, but the vague growth mechanism impedes the photovoltaic device development. In this study, γ-CsPbI₃ films are directly obtained through co-evaporation at 50 °C without any additives or high-temperature post-annealing. Focusing on the molecular thermodynamic calculations, it is proposed that the unique kinetic energy of evaporated molecules and the in-situ substrate thermal energy synergistically provide the energy prerequisite for γ-CsPbI₃ formation. Furthermore, the γ phase stabilization is clarified by the crystal grain size effect with regard to the Gibbs free energy difference between the γ and δ phases, which is adjusted through substrate temperature and evaporation rate. The obtained p-i-n device realizes an efficiency of 12.75%, which is the highest value for the thermally evaporated γ-CsPbI₃ photovoltaics at low temperature without additives. This study deepens the understanding of thermal evaporation process, benefiting to high-performance CsPbI₃-textured silicon tandem photovoltaics.

A comprehensive overview on the state-of-the-art progress of the emerging 2D MA₂Z₄ family is presented. The versatile properties including mechanics, optics, thermal transport, piezoelectrical effect, electronics, and magnetics are elaborated. The property tunability is also revealed by substitution/doping, strain engineering, and layered strategy. Theoretical and experimental attempts or advances in applying 2D MA₂Z₄ to transistors/spintronics, photocatalysts, batteries, and gas sensors are then reviewed to show its prospective applications over a vast territory.

Abstract

The discovery of 2D layered MoSi₂N₄ and WSi₂N₄ without knowing their 3D parents by chemical vapor deposition in 2020 has stimulated extensive studies of 2D MA₂Z₄ system due to its structural complexity and diversity as well as versatile and intriguing properties. Here, a comprehensive overview on the state-of-the-art progress of this 2D MA₂Z₄ family is presented. Starting by describing the unique sandwich structural characteristics of the emerging monolayer MA₂Z₄, their versatile properties including mechanics, piezoelectricity, thermal transport, electronics, optics/optoelectronics, and magnetism is summarized and anatomized. The property tunability via strain engineering, surface functionalization and layered strategy is also elaborated. Theoretical and experimental attempts or advances in applying 2D MA₂Z₄ to transistors, photocatalysts, batteries and gas sensors are then reviewed to show its prospective applications over a vast territory. New opportunities are further discussed and prospects are suggested for this emerging 2D family. The overview is anticipated to guide the further understanding and exploration on 2D MA₂Z₄.

Nature Communications, Published online: 31 March 2023; doi:10.1038/s41467-023-37482-0

The standard topological insulator is characterized by an insulating bulk and a conducting boundary, so a three dimensional insulating bulk of a topological insulator has a conducting surface. Recently, this idea was extended to the edges of the surfaces of the three dimensional material as a new topological phase, referred to as a higher-order topological insulator. Here, the authors find evidence of such higher order topological insulator states in tungsten ditelluride using heterostructures composed of tungsten ditelluride and graphene.

Nature Communications, Published online: 30 March 2023; doi:10.1038/s41467-023-37603-9

When entering a ferromagnet, a spin-singlet supercurrent decays rapidly, while a spin-triplet supercurrent can extend over much longer distances. Here, the authors observe long-range, spin triplet supercurrent in lateral Josephson junctions constructed using the van der Waals metallic ferromagnet Fe3GeTe2 as the weak link.

Nature Communications, Published online: 30 March 2023; doi:10.1038/s41467-023-37495-9

A quantized plateau is typically considered to be the feature of a fractional quantum Hall state. Yan et al. report a series of plateaus quantized at unusual fractions in a confined two-dimensional electron gas, which is attributed to enhanced density in the confined region.

Er³⁺ 1.54-µm electroluminescence based on the CsPbCl₃ perovskite films for photonic devices operating in the third telecommunication window is realized through energy transfer from Yb³⁺activated by CsPbCl₃ via a quantum cutting process to Er³⁺. The obtained peak external quantum efficiency far exceeds that of the Er³⁺-based organic light emitting diode by two orders of magnitude.

Abstract

Erbium ions (Er³⁺, 1.54 µm) electric pumped light sources with excellent optical properties and a simple fabrication process are urgently desired to satisfy the development of silicon-based integration photonics. The previous Er-based electroluminescence devices are mainly based on Er-complexes or Er-doped oxide compounds, which usually suffer from low external quantum efficiency(EQE)or high applied voltage etc. In this work, a novel type of Er³⁺/Yb³⁺ co-doped lead-halide perovskite films (Er³⁺/Yb³⁺:CsPbCl₃) with the maximum photoluminescence quantum yield of 30.12% are prepared by a simple two-step solution-coating method and the corresponding light emitting diodes (Er-PeLEDs) are fabricated, which demonstrate an almost pure 1.54-µm emission and a peak EQE up to 0.366% at a low applied voltage of 1.4 V. Strong negative thermal quenching effect may help Er-PeLEDs suppress Joule heating quenching. These excellent LED properties benefit mainly from the outstanding regulatory performance of acetate to perovskite films, the excellent semiconductor behavior and strong ionic property of the perovskite, and the involvement of Yb³⁺ ions, which can directly and efficiently transfer the exciton energy to Er³⁺ through a quantum cutting process. Overall, the realization of 1.54-µm Er-PeLEDs offers new opportunities for silicon-based integrated light sources.

Nature, Published online: 29 March 2023; doi:10.1038/s41586-023-05759-5

Chips with 256 × 256 memristor arrays that were monolithically integrated on complementary metal–oxide–semiconductor (CMOS) circuits in a commercial foundry achieved 2,048 conductance levels in individual memristors.

Advanced Materials, Volume 35, Issue 13, March 29, 2023.

Nature Electronics, Published online: 28 March 2023; doi:10.1038/s41928-023-00953-9

Micro-light-emitting diodes — microLEDs — could be used to create the next generation of displays, for use in smartwatches and augmented reality devices, if various fabrication issues can be addressed.

Nature Electronics, Published online: 28 March 2023; doi:10.1038/s41928-023-00945-9

AI chips that flip

A high-performance, high-stability, and low-cost Te_0.7Se_0.3 infrared photodiode is fabricated throughcomplementary metal–oxide–semiconductor (CMOS)-compatible low-temperature thermal evaporation. The device achieves the fastest response among Te-based photodiodes, a low dark current density , the ability of matter identification, and superior electrical and thermal stabilities. This work paves a new way for CMOS-compatible infrared imagers.

Abstract

Short-wave infrared detectors are increasingly important in the fields of autonomous driving, food safety, disease diagnosis, and scientific research. However, mature short-wave infrared cameras such as InGaAs have the disadvantage of complex heterogeneous integration with complementary metal–oxide–semiconductor (CMOS) readout circuits, leading to high cost and low imaging resolution. Herein, a low-cost, high-performance, and high-stability Te _x Se_{1– x} short-wave infrared photodiode detector is reported. The Te _x Se_{1– x} thin film is fabricated through CMOS-compatible low-temperature evaporation and post-annealing process, showcasing the potential of direct integration on the readout circuit. The device demonstrates a broad-spectrum response of 300–1600 nm, a room-temperature specific detectivity of 1.0 × 10¹⁰ Jones, a −3 dB bandwidth up to 116 kHz, and a linear dynamic range of over 55 dB, achieving the fastest response among Te-based photodiode devices and a dark current density 7 orders of magnitude smaller than Te-based photoconductive and field-effect transistor devices. With a simple Si₃N₄ packaging, the detector shows high electric stability and thermal stability, meeting the requirements for vehicular applications. Based on the optimized Te _x Se_{1– x} photodiode detector, the applications in material identification and masking imaging is demonstrated. This work paves a new way for CMOS-compatible infrared imaging chips.