Absence of near-ambient superconductivity in LuH2±xNy.

A recent study demonstrated near-ambient superconductivity in nitrogen-doped lutetium hydride1. This stimulated a worldwide interest in exploring room-temperature superconductivity at low pressures. Here, by using a high-pressure and high-temperature synthesis technique, we have obtained nitrogen-doped lutetium hydride (LuH2±xNy), which has a dark-blue colour and a structure with the space group [Formula: see text] as evidenced by X-ray diffraction. This structure is the same as that reported in ref. 1, with a slight difference in lattice constant. Raman spectroscopy of our samples also showed patterns similar to those observed in ref. 1. Energy-dispersive X-ray spectroscopy confirmed the presence of nitrogen in the samples. We observed a metallic behaviour from 350 K to 2 K at ambient pressure. On applying pressures from 2.1 GPa to 41 GPa, we observed a gradual colour change from dark blue to violet to pink-red. By measuring the resistance at pressures ranging from 0.4 GPa to 40.1 GPa, we observed a progressively improved metallic behaviour; however, superconductivity was not observed above 2 K. Temperature dependence of magnetization at high pressure shows a very weak positive signal between 100 K and 320 K, and the magnetization increases with an increase in magnetic field at 100 K. All of these are not expected for superconductivity above 100 K. Thus, we conclude the absence of near-ambient superconductivity in this nitrogen-doped lutetium hydride at pressures below 40.1 GPa.

Stack growth of wafer-scale van der Waals superconductor heterostructures.

Two-dimensional (2D) van der Waals (vdW) heterostructures have attracted considerable attention in recent years1-5. The most widely used method of fabrication is to stack mechanically exfoliated micrometre-sized flakes6-18, but this process is not scalable for practical applications. Despite thousands of 2D materials being created, using various stacking combinations1-3,19-21, hardly any large 2D superconductors can be stacked intact into vdW heterostructures, greatly restricting the applications for such devices. Here we report a high-to-low temperature strategy for controllably growing stacks of multiple-layered vdW superconductor heterostructure (vdWSH) films at a wafer scale. The number of layers of 2D superconductors in the vdWSHs can be precisely controlled, and we have successfully grown 27 double-block, 15 triple-block, 5 four-block and 3 five-block vdWSH films (where one block represents one 2D material). Morphological, spectroscopic and atomic-scale structural analyses reveal the presence of parallel, clean and atomically sharp vdW interfaces on a large scale, with very little contamination between neighbouring layers. The intact vdW interfaces allow us to achieve proximity-induced superconductivity and superconducting Josephson junctions on a centimetre scale. Our process for making multiple-layered vdWSHs can easily be generalized to other situations involving 2D materials, potentially accelerating the design of next-generation functional devices and applications22-24.

Proton-assisted growth of ultra-flat graphene films.

Graphene films grown by chemical vapour deposition have unusual physical and chemical properties that offer promise for applications such as flexible electronics and high-frequency transistors1-10. However, wrinkles invariably form during growth because of the strong coupling to the substrate, and these limit the large-scale homogeneity of the film1-4,11,12. Here we develop a proton-assisted method of chemical vapour deposition to grow ultra-flat graphene films that are wrinkle-free. Our method of proton penetration13-17 and recombination to form hydrogen can also reduce the wrinkles formed during traditional chemical vapour deposition of graphene. Some of the wrinkles disappear entirely, owing to the decoupling of van der Waals interactions and possibly an increase in distance from the growth surface. The electronic band structure of the as-grown graphene films shows a V-shaped Dirac cone and a linear dispersion relation within the atomic plane or across an atomic step, confirming the decoupling from the substrate. The ultra-flat nature of the graphene films ensures that their surfaces are easy to clean after a wet transfer process. A robust quantum Hall effect appears even at room temperature in a device with a linewidth of 100 micrometres. Graphene films grown by proton-assisted chemical vapour deposition should largely retain their intrinsic performance, and our method should be easily generalizable to other nanomaterials for strain and doping engineering.

Trapping Hydrogen Molecules between Perfect Graphene.

There is a lack of deep understanding of hydrogen intercalation into graphite due to many challenges faced during characterization of the systems. Therefore, a suitable route to trap isolated hydrogen molecules (H2) between the perfect graphite lattices needs to be found. Here we realize the formation of hydrogen bubbles in graphite with controllable density, size, and layer number. We find that the molecular H2 cannot be diffused between nor escape from the defect-free graphene lattices, and it remains stable in the pressurized bubbles up to 400 °C. The internal pressure of H2 inside the bubbles is strongly temperature dependent, and it decreases as the temperature rises. The proton permeation rate can be estimated at a specific plasma power. The producing method of H2 bubbles offers a useful way for storing hydrogen in layered materials, and these materials provide a prospective research platform for studying nontrivial quantum effects in confined H2.

Axial-Bonding-Driven Dimensionality Effect on the Charge-Density Wave in NbSe2.

2H-NbSe2 is a prototypical charge-density-wave (CDW) system, exhibiting such a symmetry-breaking quantum ground state in its bulk and down to a single-atomic-layer limit. However, how this state depends on dimensionality and what governs the dimensionality effect remain controversial. Here, we experimentally demonstrate a robust 3 × 3 CDW phase in both freestanding and substrate-supported bilayer NbSe2, far above the bulk transition temperature. We exclude environmental effects and reveal a strong temperature and thickness dependence of Raman intensity from an axially vibrating A1g phonon mode, involving Se ions. Using first-principles calculations, we show that these result from a delicate but profound competition between the intra- and interlayer bonding formed between Se-pz orbitals. Our results suggest the crucial role of Se out-of-plane displacement in driving the CDW distortion, revealing the Se-dominated dimensionality effect and establishing a new perspective on the chemical bonding and mechanical stability in layered CDW materials.

From Esters to Ketones via a Photoredox-Assisted Reductive Acyl Cross-Coupling Strategy.

A method was developed for ketone synthesis via a photoredox-assisted reductive acyl cross-coupling (PARAC) using a nickel/photoredox dual-catalyzed cross-electrophile coupling of two different carboxylic acid esters. A variety of aryl, 1°, 2°, 3°-alkyl 2-pyridyl esters can act as acyl electrophiles while N-(acyloxy)phthalimides (NHPI esters) act as 1°, 2°, 3°-radical precursors. Our PARAC strategy provides an alternative and reliable way to synthesize various sterically congested 3°-3°, 3°-2°, and aryl-3° ketones under mild and highly unified conditions, which have been otherwise difficult to access. The combined experimental and computational studies identified a Ni0 /NiI /NiIII pathway for ketone formation.

Growth of environmentally stable transition metal selenide films.

Two-dimensional transition metal selenides (TMSs) possess fascinating physical properties. However, many as-prepared TMSs are environmentally unstable and limited in sample size, which greatly hinder their wide applications in high-performance electrical devices. Here we develop a general two-step vapour deposition method and successfully grow different TMS films with controllable thickness, wafer size and high quality. The superconductivity of the grown NbSe2 film is comparable with sheets exfoliated from bulk materials, and can maintain stability after a variety of harsh treatments, which are ascribed to the absence of oxygen during the whole growth process. Such environmental stability can greatly simplify the fabrication procedure for device applications, and should be of both fundamental and technological significance in developing TMS-based devices.

Selective 1,2-Aryl-Aminoalkylation of Alkenes Enabled by Metallaphotoredox Catalysis.

A highly chemo- and regioselective intermolecular 1,2-aryl-aminoalkylation of alkenes by photoredox/nickel dual catalysis is described here. This three-component conjunctive cross-coupling is highlighted by its first application of primary alkyl radicals, which were not compatible in previous reports. The readily prepared α-silyl amines could be transferred to α-amino radicals by photo-induced single electron transfer step. The radical addition/cross-coupling cascade reaction proceeds under mild, base-free and redox-neutral conditions with good functional group tolerance, and importantly, provides an efficient and concise method for the synthesis of structurally valuable α-aryl substituted γ-amino acid derivatives motifs.

An unusual continuous paramagnetic-limited superconducting phase transition in 2D NbSe 2.

Time reversal and spatial inversion are two key symmetries for conventional Bardeen-Cooper-Schrieffer (BCS) superconductivity 1 . Breaking inversion symmetry can lead to mixed-parity Cooper pairing and unconventional superconducting properties1-5. Two-dimensional (2D) NbSe2 has emerged as a new non-centrosymmetric superconductor with the unique out-of-plane or Ising spin-orbit coupling (SOC)6-9. Here we report the observation of an unusual continuous paramagnetic-limited superconductor-normal metal transition in 2D NbSe2. Using tunelling spectroscopy under high in-plane magnetic fields, we observe a continuous closing of the superconducting gap at the upper critical field at low temperatures, in stark contrast to the abrupt first-order transition observed in BCS thin-film superconductors10-12. The paramagnetic-limited continuous transition arises from a large spin susceptibility of the superconducting phase due to the Ising SOC. The result is further supported by self-consistent mean-field calculations based on the ab initio band structure of 2D NbSe2. Our findings establish 2D NbSe2 as a promising platform to explore novel spin-dependent superconducting phenomena and device concepts 1 , such as equal-spin Andreev reflection 13 and topological superconductivity14-16.

Metal- and radical-free aerobic oxidation of heteroaromatic methanes: an efficient synthesis of heteroaromatic aldehydes.

A metal-free and radical-free synthesis of heteroaromatic aldehydes was developed through aerobic oxidation of methyl groups in an I2/DMSO/O2 catalytic system. Under the reaction conditions, various functional groups such as methoxy, aldehyde, ester, nitro, amide, and halo (F, Cl, Br) groups were well tolerated. The bioactive compounds like chlorchinaldin derivative and papaverine were also oxidized to the corresponding aldehydes and ketones. This reaction provided an efficient method for preparing the valuable heteroaromatic aldehydes.

Gate Tuning of Electronic Phase Transitions in Two-Dimensional NbSe_{2}.

Recent experimental advances in atomically thin transition metal dichalcogenide (TMD) metals have unveiled a range of interesting phenomena including the coexistence of charge-density-wave (CDW) order and superconductivity down to the monolayer limit. The atomic thickness of two-dimensional (2D) TMD metals also opens up the possibility for control of these electronic phase transitions by electrostatic gating. Here, we demonstrate reversible tuning of superconductivity and CDW order in model 2D TMD metal NbSe_{2} by an ionic liquid gate. A variation up to ∼50% in the superconducting transition temperature has been observed. Both superconductivity and CDW order can be strengthened (weakened) by increasing (reducing) the carrier density in 2D NbSe_{2}. The doping dependence of these phase transitions can be understood as driven by a varying electron-phonon coupling strength induced by the gate-modulated carrier density and the electronic density of states near the Fermi surface.

Bulk signatures of pressure-induced band inversion and topological phase transitions in Pb(1-x)Sn(x)Se.

The characteristics of topological insulators are manifested in both their surface and bulk properties, but the latter remain to be explored. Here we report bulk signatures of pressure-induced band inversion and topological phase transitions in Pb(1-x)Sn(x)Se (x=0.00, 0.15, and 0.23). The results of infrared measurements as a function of pressure indicate the closing and the reopening of the band gap as well as a maximum in the free carrier spectral weight. The enhanced density of states near the band gap in the topological phase gives rise to a steep interband absorption edge. The change of density of states also yields a maximum in the pressure dependence of the Fermi level. Thus, our conclusive results provide a consistent picture of pressure-induced topological phase transitions and highlight the bulk origin of the novel properties in topological insulators.

Predictive potential of preoperative Naples prognostic score-based nomogram model for the prognosis in surgical resected thoracic esophageal squamous cell carcinoma patients: A retrospective cohort study.

The present study aimed to establish an effective prognostic nomogram model based on the Naples prognostic score (NPS) for resectable thoracic esophageal squamous cell carcinoma (ESCC). A total of 277 patients with ESCC, who underwent standard curative esophagectomy and designated as study cohort, were retrospectively analyzed. The patients were divided into different groups, including NPS 0, NPS 1, NPS 2, and NPS 3 or 4 groups, for further analysis, and the results were validated in an external cohort of 122 ESCC patients, who underwent surgery at another cancer center. In our multivariate analysis of the study cohort showed that the tumor-node-metastasis (TNM) stage, systemic inflammation score, and NPS were the independent prognostic factors for the overall survival (OS) and progression-free survival (PFS) durations. In addition, the differential grade was also an independent prognostic factor for the OS in the patients with ESCC after surgery (all P < .05). The area under the curve of receiver operator characteristics for the PFS and OS prediction with systemic inflammation score and NPS were 0.735 (95% confidence interval [CI] 0.676-0.795, P < .001) and 0.835 (95% CI 0.786-0.884, P < .001), and 0.734 (95% CI 0.675-0.793, P < .001) and 0.851 (95% CI 0.805-0.896, P < .001), respectively. The above independent predictors for OS or PFS were all selected in the nomogram model. The concordance indices (C-indices) of the nomogram models for predicting OS and PFS were 0.718 (95% CI 0.681-0.755) and 0.669 (95% CI 0.633-0.705), respectively, which were higher than that of the 7th edition of American Joint Committee on Cancer TNM staging system [C-index 0.598 (95% CI 0.558-0.638) for OS and 0.586 (95% CI 0.546-0.626) for PFS]. The calibration curves for predicting the 5-year OS or PFS showed a good agreement between the prediction by nomogram and actual observation. In the external validation cohort, the nomogram discrimination for OS was better than that of the 7th edition of TNM staging systems [C-index: 0.697 (95% CI 0.639-0.755) vs 0.644 (95% CI 0.589-0.699)]. The calibration curves showed good consistency in predicting the 5-year survival between the actual observation and nomogram predictions. The decision curve also showed a higher potential of the clinical application of predicting the 5-years OS of the proposed nomogram model as compared to that of the 7th edition of TNM staging systems. The preoperative NPS-based nomogram model had a certain potential role for predicting the prognosis of ESCC patients.

Defect-induced helicity dependent terahertz emission in Dirac semimetal PtTe2 thin films.

Nonlinear transport enabled by symmetry breaking in quantum materials has aroused considerable interest in condensed matter physics and interdisciplinary electronics. However, achieving a nonlinear optical response in centrosymmetric Dirac semimetals via defect engineering has remained a challenge. Here, we observe the helicity dependent terahertz emission in Dirac semimetal PtTe2 thin films via the circular photogalvanic effect under normal incidence. This is activated by a controllable out-of-plane Te-vacancy defect gradient, which we unambiguously evidence with electron ptychography. The defect gradient lowers the symmetry, which not only induces the band spin splitting but also generates the giant Berry curvature dipole responsible for the circular photogalvanic effect. We demonstrate that the THz emission can be manipulated by the Te-vacancy defect concentration. Furthermore, the temperature evolution of the THz emission features a minimum in the THz amplitude due to carrier compensation. Our work provides a universal strategy for symmetry breaking in centrosymmetric Dirac materials for efficient nonlinear transport.

Signatures of a pressure-induced topological quantum phase transition in BiTeI.

We report the observation of two signatures of a pressure-induced topological quantum phase transition in the polar semiconductor BiTeI using x-ray powder diffraction and infrared spectroscopy. The x-ray data confirm that BiTeI remains in its ambient-pressure structure up to 8 GPa. The lattice parameter ratio c/a shows a minimum between 2.0-2.9 GPa, indicating an enhanced c-axis bonding through p(z) band crossing as expected during the transition. Over the same pressure range, the infrared spectra reveal a maximum in the optical spectral weight of the charge carriers, reflecting the closing and reopening of the semiconducting band gap. Both of these features are characteristics of a topological quantum phase transition and are consistent with a recent theoretical proposal.

Long non-coding RNA GNAS-AS1 knockdown inhibits proliferation and epithelial-mesenchymal transition of lung adenocarcinoma cells via the microRNA-433-3p/Rab3A axis.

The goal of this study was to demonstrate the functions and specific mechanism of long non-coding RNA (lncRNA) GNAS-AS1 in lung adenocarcinoma. Levels of lncRNA GNAS-AS1, microRNA (miR)-433-3p, and Rab3A were assessed by quantitative real-time PCR (qRT-PCR). The target-binding sites of lncRNA GNAS-AS1, miR-433-3p, and Rab3A were predicted and confirmed by bioinformatics tool (StarBase) and a dual-luciferase reporter system. Cell proliferation and apoptosis were checked using MTT and flow cytometry, respectively. Additionally, the levels of apoptosis-related and epithelial-mesenchymal transition (EMT)-associated genes in A549 cells were analyzed by qRT-PCR and western blot. We found that lncRNA GNAS-AS1 was upregulated, miR-433-3p was low-expressed, and Rab3A was overexpressed in lung adenocarcinoma tissues and cell lines. LncRNA GNAS-AS1 interacted with miR-433-3p and negatively regulated miR-433-3p levels. Rab3A was a direct target of miR-433-3p. Downregulation of lncRNA GNAS-AS1 remarkably suppressed cell proliferation, promoted cell apoptosis, decreased B-cell lymphoma-2 (Bcl-2) expression, enhanced the Bcl-2-Associated X (Bax) level, promoted E-cadherin expression, and reduced N-cadherin and Rab3A levels. However, the miR-433-3p inhibitor reversed all these findings. Similarly, the inhibitory effects of miR-433-3p mimic on A549 cells were reversed by the Rab3A-plasmid. In conclusion, lncRNA GNAS-AS1 downregulation suppressed lung adenocarcinoma cell proliferation and EMT through the miR-433-3p/Rab3A axis.

Thickness-Dependent Evolutions of Surface Reconstruction and Band Structures in Epitaxial ß-In2Se3 Thin Films.

Ferroelectric materials have received great attention in the field of data storage, benefiting from their exotic transport properties. Among these materials, the two-dimensional (2D) In2Se3 has been of particular interest because of its ability to exhibit both in-plane and out-of-plane ferroelectricity. In this article, we realized the molecular beam epitaxial (MBE) growth of ß-In2Se3 films on bilayer graphene (BLG) substrates with precisely controlled thickness. Combining in situ scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES) measurements, we found that the four-monolayer ß-In2Se3 is a semiconductor with a (9 × 1) reconstructed superlattice. In contrast, the monolayer ß-In2Se3/BLG heterostructure does not show any surface reconstruction due to the interfacial interaction and moiré superlattice, which instead results in a folding Dirac cone at the center of the Brillouin zone. In addition, we found that the band gap of In2Se3 film decreases after potassium doping on its surface, and the valence band maximum also shifts in momentum after surface potassium doping. The successful growth of high-quality ß-In2Se3 thin films would be a new platform for studying the 2D ferroelectric heterostructures and devices. The experimental results on the surface reconstruction and band structures also provide important information on the quantum confinement and interfacial effects in the epitaxial ß-In2Se3 films.

An anisotropic van der Waals dielectric for symmetry engineering in functionalized heterointerfaces.

Van der Waals dielectrics are fundamental materials for condensed matter physics and advanced electronic applications. Most dielectrics host isotropic structures in crystalline or amorphous forms, and only a few studies have considered the role of anisotropic crystal symmetry in dielectrics as a delicate way to tune electronic properties of channel materials. Here, we demonstrate a layered anisotropic dielectric, SiP2, with non-symmorphic twofold-rotational C2 symmetry as a gate medium which can break the original threefold-rotational C3 symmetry of MoS2 to achieve unexpected linearly-polarized photoluminescence and anisotropic second harmonic generation at SiP2/MoS2 interfaces. In contrast to the isotropic behavior of pristine MoS2, a large conductance anisotropy with an anisotropy index up to 1000 can be achieved and modulated in SiP2-gated MoS2 transistors. Theoretical calculations reveal that the anisotropic moiré potential at such interfaces is responsible for the giant anisotropic conductance and optical response. Our results provide a strategy for generating exotic functionalities at dielectric/semiconductor interfaces via symmetry engineering.

Berry curvature dipole generation and helicity-to-spin conversion at symmetry-mismatched heterointerfaces.

The Berry curvature dipole (BCD) is a key parameter that describes the geometric nature of energy bands in solids. It defines the dipole-like distribution of Berry curvature in the band structure and plays a key role in emergent nonlinear phenomena. The theoretical rationale is that the BCD can be generated at certain symmetry-mismatched van der Waals heterointerfaces even though each material has no BCD in its band structure. However, experimental confirmation of such a BCD induced via breaking of the interfacial symmetry remains elusive. Here we demonstrate a universal strategy for BCD generation and observe BCD-induced gate-tunable spin-polarized photocurrent at WSe2/SiP interfaces. Although the rotational symmetry of each material prohibits the generation of spin photocurrent under normal incidence of light, we surprisingly observe a direction-selective spin photocurrent at the WSe2/SiP heterointerface with a twist angle of 0°, whose amplitude is electrically tunable with the BCD magnitude. Our results highlight a BCD-spin-valley correlation and provide a universal approach for engineering the geometric features of twisted heterointerfaces.

Electrical switching of ferro-rotational order in nanometre-thick 1T-TaS2 crystals.

Hysteretic switching of domain states is a salient characteristic of all ferroic materials and the foundation for their multifunctional applications. Ferro-rotational order is emerging as a type of ferroic order that features structural rotations, but control over state switching remains elusive due to its invariance under both time reversal and spatial inversion. Here we demonstrate electrical switching of ferro-rotational domain states in the charge-density-wave phases of nanometre-thick 1T-TaS2 crystals. Cooling from the high-symmetry phase to the ferro-rotational phase under an external electric field induces domain state switching and domain wall formation, which is realized in a simple two-terminal configuration using a volt-scale bias. Although the electric field does not couple with the order due to symmetry mismatch, it drives domain wall propagation to give rise to reversible, durable and non-volatile isothermal state switching at room temperature. These results offer a route to the manipulation of ferro-rotational order and its nanoelectronic applications.