Evidence for electron-hole crystals in a Mott insulator.

The coexistence of correlated electron and hole crystals enables the realization of quantum excitonic states, capable of hosting counterflow superfluidity and topological orders with long-range quantum entanglement. Here we report evidence for imbalanced electron-hole crystals in a doped Mott insulator, namely, α-RuCl3, through gate-tunable non-invasive van der Waals doping from graphene. Real-space imaging via scanning tunnelling microscopy reveals two distinct charge orderings at the lower and upper Hubbard band energies, whose origin is attributed to the correlation-driven honeycomb hole crystal composed of hole-rich Ru sites and rotational-symmetry-breaking paired electron crystal composed of electron-rich Ru-Ru bonds, respectively. Moreover, a gate-induced transition of electron-hole crystals is directly visualized, further corroborating their nature as correlation-driven charge crystals. The realization and atom-resolved visualization of imbalanced electron-hole crystals in a doped Mott insulator opens new doors in the search for correlated bosonic states within strongly correlated materials.

Polyene phosphatidylcholine promotes tibial fracture healing in rats by stimulating angiogenesis dominated by the VEGFA/VEGFR2 signaling pathway.

One of the factors that predispose to fractures is liver damage. Interestingly, fractures are sometimes accompanied by abnormal liver function. Polyene phosphatidylcholine (PPC) is an important liver repair drug. We wondered if PPC had a role in promoting fracture healing. A rat model of tibial fracture was developed using the modified Einhorn model method. X-rays were used to detect the progression of fracture healing. Progress of ossification and angiogenesis at the fracture site were analyzed by Safranin O/fast green staining and CD31 immunohistochemistry. To investigate whether PPC has a direct angiogenesis effect, HUVECs were used. We performed MTT, wound healing, Transwell migration, and tube formation assays. Finally, RT-qPCR and Western blot analysis were used to study the underlying mechanism. The results showed that PPC significantly shortened the apparent recovery time of mobility in rats. PPC treatment significantly promoted the formation of cartilage callus, endochondral ossification, and angiogenesis at the fracture site. In vitro, PPC promoted the proliferative viability of HUVECs, their ability to heal wounds, and their ability to penetrate membranes in the Transwell apparatus and increased the tube formation of cells. The transcription of VEGFA, VEGFR2, PLCγ, RAS, ERK1/2 and MEK1/2 was significantly up regulated by PPC. Further, the protein level results demonstrated a significant increase in the expression of VEGFA, VEGFR2, MEK1/2, and ERK1/2 proteins. In conclusion, our findings suggest that PPC promotes angiogenesis by activating the VEGFA/VEGFR2 and downstream signaling pathway, thereby accelerating fracture healing.

Beyond Conventional Charge Density Wave for Strongly Enhanced 2D Superconductivity in 1H-TaS2 Superlattices.

Noncentrosymmetric transition metal dichalcogenide (TMD) monolayers offer a fertile platform for exploring unconventional Ising superconductivity (SC) and charge density waves (CDWs). However, the vulnerability of isolated monolayers to structural disorder and environmental oxidation often degrade their electronic coherence. Herein, an alternative approach is reported for fabricating stable and intrinsic monolayers of 1H-TaS2 sandwiched between SnS blocks in a (SnS)1.15TaS2 van der Waals (vdW) superlattice. The SnS block layers not only decouple individual 1H-TaS2 sublayers to endow them with monolayer-like electronic characteristics, but also protect the 1H-TaS2 layers from electronic degradation. The results reveal the characteristic 3 × 3 CDW order in 1H-TaS2 sublayers associated with electronic rearrangement in the low-lying sulfur p band, which uncovers a previously undiscovered CDW mechanism rather than the conventional Fermi surface-related framework. Additionally, the (SnS)1.15TaS2 superlattice exhibits a strongly enhanced Ising-like SC with a layer-independent Tc of ≈3.0 K, comparable to that of the isolated monolayer 1H-TaS2 sample, presumably attributed to their monolayer-like characteristics and retained Fermi states. These results provide new insights into the long-debated CDW order and enhanced SC of monolayer 1H-TaS2, establishing bulk vdW superlattices as promising platforms for investigating exotic collective quantum phases in the 2D limit.

Resonant Raman scattering of few layers CrBr3.

We investigate the vibrational and magnetic properties of thin layers of chromium tribromide (CrBr3) with a thickness ranging from three to twenty layers (3-20 L) revealed by the Raman scattering (RS) technique. Systematic dependence of the RS process efficiency on the energy of the laser excitation is explored for four different excitation energies: 1.96 eV, 2.21 eV, 2.41 eV, and 3.06 eV. Our characterization demonstrates that for 12 L CrBr3, 3.06 eV excitation could be considered resonant with interband electronic transitions due to the enhanced intensity of the Raman-active scattering resonances and the qualitative change in the Raman spectra. Polarization-resolved RS measurements for 12 L CrBr3 and first-principles calculations allow us to identify five observable phonon modes characterized by distinct symmetries, classified as the A g and E g modes. The evolution of phonon modes with temperature for a 16 L CrBr3 encapsulated in hexagonal boron nitride flakes demonstrates alterations of phonon energies and/or linewidths of resonances indicative of a transition between the paramagnetic and ferromagnetic state at Curie temperature ( T C ≈ 50  K). The exploration of the effects of thickness on the phonon energies demonstrated small variations pronounces exclusively for the thinnest layers in the vicinity of 3-5 L. We propose that this observation can be due to the strong localization in the real space of interband electronic excitations, limiting the effects of confinement for resonantly excited Raman modes to atomically thin layers.

Quasi van der Waals Epitaxy of Single Crystalline GaN on Amorphous SiO2/Si(100) for Monolithic Optoelectronic Integration.

The realization of high quality (0001) GaN on Si(100) is paramount importance for the monolithic integration of Si-based integrated circuits and GaN-enabled optoelectronic devices. Nevertheless, thorny issues including large thermal mismatch and distinct crystal symmetries typically bring about uncontrollable polycrystalline GaN formation with considerable surface roughness on standard Si(100). Here a breakthrough of high-quality single-crystalline GaN film on polycrystalline SiO2/Si(100) is presented by quasi van der Waals epitaxy and fabricate the monolithically integrated photonic chips. The in-plane orientation of epilayer is aligned throughout a slip and rotation of high density AlN nuclei due to weak interfacial forces, while the out-of-plane orientation of GaN can be guided by multi-step growth on transfer-free graphene. For the first time, the monolithic integration of light-emitting diode (LED) and photodetector (PD) devices are accomplished on CMOS-compatible SiO2/Si(100). Remarkably, the self-powered PD affords a rapid response below 250 µs under adjacent LED radiation, demonstrating the responsivity and detectivity of 2.01 × 105 A/W and 4.64 × 1013 Jones, respectively. This work breaks a bottleneck of synthesizing large area single-crystal GaN on Si(100), which is anticipated to motivate the disruptive developments in Si-integrated optoelectronic devices.

Topological Spin Textures in an Insulating van der Waals Ferromagnet.

Generation and control of topological spin textures constitutes one of the most exciting challenges of modern spintronics given their potential applications in information storage technologies. Of particular interest are magnetic insulators, which due to low damping, absence of Joule heating and reduced dissipation can provide energy-efficient spin-textures platform. Here, it is demonstrated that the interplay between sample thickness, external magnetic fields, and optical excitations can generate a prolific paramount of spin textures, and their coexistence in insulating CrBr3 van der Waals (vdW) ferromagnets. Using high-resolution magnetic force microscopy and large-scale micromagnetic simulation methods, the existence of a large region in T-B phase diagram is demonstrated where different stripe domains, skyrmion crystals, and magnetic domains exist and can be intrinsically selected or transformed to each-other via a phase-switch mechanism. Lorentz transmission electron microscopy unveils the mixed chirality of the magnetic textures that are of Bloch-type at given conditions but can be further manipulated into Néel-type or hybrid-type via thickness-engineering. The topological phase transformation between the different magnetic objects can be further inspected by standard photoluminescence optical probes resolved by circular polarization indicative of an existence of exciton-skyrmion coupling mechanism. The findings identify vdW magnetic insulators as a promising framework of materials for the manipulation and generation of highly ordered skyrmion lattices relevant for device integration at the atomic level.

Optical properties of orthorhombic germanium sulfide: unveiling the anisotropic nature of Wannier excitons.

To fully explore exciton-based applications and improve their performance, it is essential to understand the exciton behavior in anisotropic materials. Here, we investigate the optical properties of anisotropic excitons in GeS encapsulated by h-BN using different approaches that combine polarization- and temperature-dependent photoluminescence (PL) measurements, ab initio calculations, and effective mass approximation (EMA). Using the Bethe-Salpeter Equation (BSE) method, we found that the optical absorption spectra in GeS are significantly affected by the Coulomb interaction included in the BSE method, which shows the importance of excitonic effects besides it exhibits a significant dependence on the direction of polarization, revealing the anisotropic nature of bulk GeS. By combining ab initio calculations and EMA methods, we investigated the quasi-hydrogenic exciton states and oscillator strength (OS) of GeS along the zigzag and armchair axes. We found that the anisotropy induces lifting of the degeneracy and mixing of the excitonic states in GeS, which results in highly non-hydrogenic features. A very good agreement with the experiment is observed.

Estimating residual undifferentiated cells in human chemically induced pluripotent stem cell derived islets using lncRNA as biomarkers.

Human pluripotent stem cells (hPSCs) can generate insulin-producing beta cells for diabetes treatment, but residual undifferentiated cells may cause tumors. We developed a highly sensitive assay to detect these cells in islet cells derived from human chemically induced pluripotent stem cells (hCiPSCs), which are transgene-free and safer. We used RNA-seq data to find protein-coding and non-coding RNAs that were only expressed in hCiPSCs, not in islet cells. We confirmed these biomarkers by RT-qPCR and ddPCR. We chose long non-coding RNA (lncRNA) markers, which performed better than protein-coding RNA markers. We found that LNCPRESS2, LINC00678 and LOC105370482 could detect 1, 1 and 3 hCiPSCs in 106 islet cells by ddPCR, respectively. We tested our method on several hCiPSC lines, which could quantify 0.0001% undifferentiated cell in 106 islet cells by targeting hCiPSCs-specific lncRNA transcripts, ensuring the safety and quality of hCiPSC-derived islet cells for clinical use.

Identification and Analysis of the Expression of the PIP5K Gene Family in Tomatoes.

To explore the function of phosphatidylinositol 4-phosphate 5-kinase (PIP5K) in tomatoes, members of the tomato PIP5K family were identified and characterized using bioinformatic methods, and their expression patterns were also analyzed under salt stress and in different tissues. Twenty-one PIP5K members-namely, SlPIP5K1-SlPIP5K21-were identified from ten chromosomes, and these were divided into three groups according to a phylogenetic analysis. Further bioinformatic analysis showed four pairs of collinear relationships and fragment replication events among the SlPIP5K family members. To understand the possible roles of the SlPIP5Ks, a cis-acting element analysis was conducted, which indicated that tomato PIP5Ks could be associated with plant growth, hormones, and stress responses. We further validated the results of the in silico analysis by integrating RNA-seq and qRT-PCR techniques for salt- and hormone-treated tomato plants. Our results showed that SlPIP5K genes exhibited tissue- and treatment-specific patterns, and some of the SlPIP5Ks exhibited significantly altered expressions after our treatments, suggesting that they might be involved in these stresses. We selected one of the SlPIP5Ks that responded to our treatments, SlPIP5K2, to further understand its subcellular localization. Our results showed that SlPIP5K2 was located on the membrane. This study lays a foundation for the analysis of the biological functions of the tomato SlPIP5K genes and can also provide a theoretical basis for the selection and breeding of new tomato varieties and germplasm innovation, especially under salt stress.

Gate-Tunable Resonance State and Screening Effects for Proton-Like Atomic Charge in Graphene.

The ability to create a robust and well-defined artificial atomic charge in graphene and understand its carrier-dependent electronic properties represents an important goal toward the development of graphene-based quantum devices. Herein, we devise a new pathway toward the atomically precise embodiment of point charges into a graphene lattice by posterior (N) ion implantation into a back-gated graphene device. The N dopant behaves as an in-plane proton-like charge manifested by formation of the characteristic resonance state in the conduction band. Scanning tunneling spectroscopy measurements at varied charge carrier densities reveal a giant energetic renormalization of the resonance state up to 220 meV with respect to the Dirac point, accompanied by the observation of gate-tunable long-range screening effects close to individual N dopants. Joint density functional theory and tight-binding calculations with modified perturbation potential corroborate experimental findings and highlight the short-range character of N-induced perturbation.

Continuous Single-Crystalline GaN Film Grown on WS2 -Glass Wafer.

Use of 2D materials as buffer layers has prospects in nitride epitaxy on symmetry mismatched substrates. However, the control of lattice arrangement via 2D materials at the heterointerface presents certain challenges. In this study, the epitaxy of single-crystalline GaN film on WS2 -glass wafer is successfully performed by using the strong polarity of WS2 buffer layer and its perfectly matching lattice geometry with GaN. Furthermore, this study reveals that the first interfacial nitrogen layer plays a crucial role in the well-constructed interface by sharing electrons with both Ga and S atoms, enabling the single-crystalline stress-free GaN, as well as a violet light-emitting diode. This study paves a way for the heterogeneous integration of semiconductors and creates opportunities to break through the design and performance limitations, which are induced by substrate restriction, of the devices.

Ultra-Broadband Strong Electromagnetic Interference Shielding with Ferromagnetic Graphene Quartz Fabric.

Flexible electromagnetic interference (EMI) shielding materials with ultrahigh shielding effectiveness (SE) are highly desirable for high-speed electronic devices to attenuate radiated emissions. For hindering interference of their internal or external EMI fields, however, a metallic enclosure suffers from relatively low SE, band-limited anti-EMI responses, poor corrosion resistance, and non-adaptability to the complex geometry of a given circuit. Here, a broadband, strong EMI shielding response fabric is demonstrated based on a highly structured ferromagnetic graphene quartz fiber (FGQF) via a modulation-doped chemical vapor deposition (CVD) growth process. The precise control of the graphitic N-doping configuration endows graphene coatings on specifically designable quartz fabric weave with both high conductivity (3906 S cm-1 ) and high magnetic responsiveness (a saturation magnetization of ≈0.14 emu g-1 under 300 K), thus attaining synergistic effect of EMI shielding and electromagnetic wave (EMW) absorption for broadband anti-EMI technology. The large-scale durable FGQF exhibits extraordinary EMI SE of ≈107 dB over a broadband frequency (1-18 GHz), by configuring ≈20 nm-thick graphene coatings on a millimeter-thick quartz fabric. This work enables the potential for development of an industrial-scale, flexible, lightweight, durable, and ultra-broadband strong shielding material in advanced applications of flexible anti-electronic reconnaissance, antiradiation, and stealthy technologies.

Atomic Mechanism of Strain Alleviation and Dislocation Reduction in Highly Mismatched Remote Heteroepitaxy Using a Graphene Interlayer.

Remote heteroepitaxy is known to yield semiconductor films with better quality. However, the atomic mechanisms in systems with large mismatches are still unclear. Herein, low-strain single-crystalline nitride films are achieved on highly mismatched (∼16.3%) sapphire via graphene-assisted remote heteroepitaxy. Because of a weaker interface potential, the in-plane compressive strain at the interface releases by 30%, and dislocations are prevented. Meanwhile, the lattice distortions in the epilayer disappear when the structure climbs over the atomic steps on substrates because graphene renders the steps smooth. In this way, the density of edge dislocations in as-grown nitride films reduces to the same level as that of the screw dislocations, which is rarely observed in heteroepitaxy. Further, the indium composition in InxGa1-xN/GaN multiquantum wells increases to ∼32%, enabling the fabrication of a yellow light-emitting diode. This study demonstrates the advantages of remote heteroepitaxy for bandgap tuning and opens opportunities for photoelectronic and electronic applications.

Graphene-driving strain engineering to enable strain-free epitaxy of AlN film for deep ultraviolet light-emitting diode.

The energy-efficient deep ultraviolet (DUV) optoelectronic devices suffer from critical issues associated with the poor quality and large strain of nitride material system caused by the inherent mismatch of heteroepitaxy. In this work, we have prepared the strain-free AlN film with low dislocation density (DD) by graphene (Gr)-driving strain-pre-store engineering and a unique mechanism of strain-relaxation in quasi-van der Waals (QvdW) epitaxy is presented. The DD in AlN epilayer with Gr exhibits an anomalous sawtooth-like evolution during the whole epitaxy process. Gr can help to enable the annihilation of the dislocations originated from the interface between AlN and Gr/sapphire by impelling a lateral two-dimensional growth mode. Remarkably, it can induce AlN epilayer to pre-store sufficient tensile strain during the early growth stage and thus compensate the compressive strain caused by hetero-mismatch. Therefore, the low-strain state of the DUV light-emitting diode (DUV-LED) epitaxial structure is realized on the strain-free AlN template with Gr. Furthermore, the DUV-LED with Gr demonstrate 2.1 times enhancement of light output power and a better stability of luminous wavelength compared to that on bare sapphire. An in-depth understanding of this work reveals diverse beneficial impacts of Gr on nitride growth and provides a novel strategy of relaxing the vital requirements of hetero-mismatch in conventional heteroepitaxy.

Direct growth of wafer-scale highly oriented graphene on sapphire.

Direct chemical vapor deposition (CVD) growth of wafer-scale high-quality graphene on dielectrics is of paramount importance for versatile applications. Nevertheless, the synthesized graphene is typically a polycrystalline film with high density of uncontrolled defects, resulting in a low carrier mobility and high sheet resistance. Here, we report the direct growth of highly oriented monolayer graphene films on sapphire wafers. Our growth strategy is achieved by designing an electromagnetic induction heating CVD operated at elevated temperature, where the high pyrolysis and migration barriers of carbon species are easily overcome. Meanwhile, the embryonic graphene domains are guided into good alignment by minimizing its configuration energy. The thus obtained graphene film accordingly manifests a markedly improved carrier mobility (~14,700 square centimeters per volt per second at 4 kelvin) and reduced sheet resistance (~587 ohms per square), which compare favorably with those from catalytic growth on polycrystalline metal foils and epitaxial growth on silicon carbide.

Van der Waals epitaxy of nearly single-crystalline nitride films on amorphous graphene-glass wafer.

Van der Waals epitaxy provides a fertile playground for the monolithic integration of various materials for advanced electronics and optoelectronics. Here, a previously unidentified nanorod-assisted van der Waals epitaxy is developed and nearly single-crystalline GaN films are first grown on amorphous silica glass substrates using a graphene interfacial layer. The epitaxial GaN-based light-emitting diode structures, with a record internal quantum efficiency, can be readily lifted off, becoming large-size flexible devices. Without the effects of the potential field from a single-crystalline substrate, we expect this approach to be equally applicable for high-quality growth of nitrides on arbitrary substrates. Our work provides a revolutionary technology for the growth of high-quality semiconductors, thus enabling the hetero-integration of highly mismatched material systems.

Electrically Controlled Thermal Radiation from Reduced Graphene Oxide Membranes.

We demonstrate a fabrication procedure of hybrid devices that consist of reduced graphene oxide films supported by porous polymer membranes that host ionic solutions. We find that we can control the thermal radiation from the surface of reduced graphene oxide through a process of electrically driven reversible ionic intercalation. Through a comparative analysis of the structural, chemical, and optical properties of our reduced graphene oxide films, we identify that the dominant mechanism leading to the intercalation-induced reduction of light emission is Pauli blocking of the interband recombination of charge carriers. We inspect the capabilities of our devices to act as a platform for the electrical control of mid-infrared photonics by observing a bias-induced reduction of apparent temperature of hot surfaces visualized through an infrared thermal camera.

The STING phase-separator suppresses innate immune signalling.

Biomolecular condensates (biocondensates) formed via liquid-liquid phase-separation of soluble proteins have been studied extensively. However, neither the phase-separation of endoplasmic reticulum (ER) transmembrane protein nor a biocondensate with organized membranous structures has been reported. Here, we have discovered a spherical ER membranous biocondensate with puzzle-like structures caused by condensation of the ER-resident stimulator of interferon genes (STING) in DNA virus-infected or 2'3'-cGAMP (cyclic GMP-AMP)-treated cells, which required STING transmembrane domains, an intrinsically disordered region (IDR) and a dimerization domain. Intracellular 2'3'-cGAMP concentrations determined STING translocation or condensation. STING biocondensates constrained STING and TBK1 (TANK binding protein 1) to prevent innate immunity from overactivation, presumably acting like a 'STING-TBK1-cGAMP sponge'. Cells expressing STING-E336G/E337G showed notably enhanced innate immune responses due to impaired STING condensation after viral infection at later stages. Microtubule inhibitors impeded the STING condensate gel-like transition and augmented type I-interferon production in DNA virus-infected cells. This membranous biocondensate was therefore named the STING phase-separator.

Graphene-Nanorod Enhanced Quasi-Van Der Waals Epitaxy for High Indium Composition Nitride Films.

The nitride films with high indium (In) composition play a crucial role in the fabrication of In-rich InGaN-based optoelectronic devices. However, a major limitation is In incorporation requiring a low temperature during growth at the expense of nitride dissociation. Here, to overcome this limitation, a strain-modulated growth method, namely the graphene (Gr)-nanorod (NR) enhanced quasi-van der Waals epitaxy, is proposed to increase the In composition in InGaN alloy. The lattice transparency of Gr enables constraint of in-plane orientation of nitride film and epitaxial relationships at the heterointerface. The Gr interlayer together with NRs buffer layer substantially reduces the stress of the GaN film by 74.4%, from 0.9 to 0.23 GPa, and thus increases the In incorporation by 30.7%. The first principles calculations confirm that the release of strain accounts for the dramatic improvement. The photoluminescence peak of multiple quantum wells shifts from 461 to 497 nm and the functionally small-sized cyan light-emitting diodes of 7 × 9 mil2 are demonstrated. These findings provide an efficient approach for the growth of In-rich InGaN film and extend the applications of nitrides in advanced optoelectronic, photovoltaic, and thermoelectric devices.