Exchange-Driven Chern States in High-Mobility Intrinsic Magnetic Topological Insulators.

The layer-dependent Chern number (C) in MnBi_{2}Te_{4} is characterized by the presence of a Weyl semimetal state in the ferromagnetic coupling. However, the influence of a key factor, namely, the exchange coupling, remains unexplored. This study focuses on characterizing the C=2 state in MnBi_{2}Te_{4}, which is classified as a higher C state resulting from the anomalous n=0 Landau levels (LLs). Our findings demonstrate that the exchange coupling parameter strongly influences the formation of this Chern state, leading to a competition between the C=1 and 2 states. Moreover, the emergence of odd-even LL sequences, resulting from the breaking of LL degeneracy, provides compelling evidence for the strong exchange coupling strength. These findings highlight the significance of the exchange coupling in understanding the behavior of Chern states and LLs in magnetic quantum systems.

Crystallographic Disorder and Strong Magnetic Anisotropy in Dy3Pt2Sb4.48.

We report the crystal growth and characterization of a rare-earth-containing material, Dy3.00(1)Pt2Sb4.48(2). This compound possesses a similar structure to the previously reported Y3Pt4Ge6, but it lacks two layers of Pt atoms. Crystallographic disorder was found in Dy3.00(1)Pt2Sb4.48(2). Additionally, the Dy-Dy framework was found to have both square net and triangular lattices. Dy3.00(1)Pt2Sb4.48(2)8 was determined to be antiferromagnetically ordered around ∼15 K while a competing antiferromagnetic sublattice also exists at lower temperature. Strong magnetic anisotropy was observed, and several metamagnetic transitions were seen in the hysteresis loops. Furthermore, the Curie-Weiss fitting revealed an unusually small effective moment of Dy, which is far below the expected value of Dy3+ (10.65 µB). This material might provide a new platform to study the relationship between crystallographic disorder and magnetism.

Nonvolatile Memristive Effect in Few-Layer CrI3 Driven by Electrostatic Gating.

The potential of memristive devices for applications in nonvolatile memory and neuromorphic computing has sparked considerable interest, particularly in exploring memristive effects in two-dimensional (2D) magnetic materials. However, the progress in developing nonvolatile, magnetic field-free memristive devices using 2D magnets has been limited. In this work, we report an electrostatic-gating-induced nonvolatile memristive effect in CrI3-based tunnel junctions. The few-layer CrI3-based tunnel junction manifests notable hysteresis in its tunneling resistance as a function of gate voltage. We further engineered a nonvolatile memristor using the CrI3 tunneling junction with low writing power and at zero magnetic field. We show that the hysteretic transport observed is not a result of trivial effects or inherent magnetic properties of CrI3. We propose a potential association between the memristive effect and the newly predicted ferroelectricity in CrI3 via gating-induced Jahn-Teller distortion. Our work illuminates the potential of 2D magnets in developing next-generation advanced computing technologies.

Bipolaronic Nature of the Pseudogap in Quasi-One-Dimensional (TaSe4)2I Revealed via Weak Photoexcitation.

The origin of the pseudogap in many strongly correlated materials has been a longstanding puzzle. Here, we present experimental evidence that many-body interactions among small Holstein polarons, i.e., the formation of bipolarons, are primarily responsible for the pseudogap in (TaSe4)2I. After weak photoexcitation of the material, we observe the appearance of both dispersive (single-particle bare band) and flat bands (single-polaron sub-bands) in the gap by using time- and angle-resolved photoemission spectroscopy. Based on Monte Carlo simulations of the Holstein model, we propose that the melting of pseudogap and emergence of new bands originate from a bipolaron to single-polaron crossover. We also observe dramatically different relaxation times for the excited in-gap states in (TaSe4)2I (∼600 fs) compared with another 1D material Rb0.3MoO3 (∼60 fs), which provides a new method for distinguishing between pseudogaps induced by polaronic or Luttinger-liquid many-body interactions.

Band Gap Narrowing in a High-Entropy Spinel Oxide Semiconductor for Enhanced Oxygen Evolution Catalysis.

High-entropy oxides (HEOs), which contain five or more metal cations that are generally thought to be randomly mixed in a crystalline oxide lattice, can exhibit unique and enhanced properties, including improved catalytic performance, due to synergistic effects. Here, we show that band gap narrowing emerges in a high-entropy aluminate spinel oxide, (Fe0.2Co0.2Ni0.2Cu0.2Zn0.2)Al2O4 (A5Al2O4). The 0.9 eV band gap of A5Al2O4 is narrower than the band gaps of all parent spinel oxides. First-principles calculations for multicomponent AAl2O4 spinels indicate that the band gap narrowing arises from the broadening of the energy distribution of the 3d states due to variations in the electronegativities and crystal field splitting across the 3d transition-metal series. As a catalyst for the oxygen evolution reaction in an alkaline electrolyte, A5Al2O4 reaches a current density of 10 mA/cm2 at an overpotential of 400 mV, outperforming all of the single-metal end members at an applied potential of 1.7 V vs RHE. Catalyst deactivation occurs after 5 h at 10 mA/cm2 and is attributed, based on elemental analysis and grazing-incidence X-ray diffraction, to the formation of a passivating layer that blocks the high-entropy oxide surface. This result helps to validate that the HEO is the active catalyst. The observation of band gap narrowing in A5Al2O4 expands the scope of synergistic properties exhibited by high-entropy materials and offers insight into the question of how the electronic structure of multicomponent oxide materials can be engineered via a high-entropy approach to achieve enhanced catalytic properties.

Layered Semiconductor Cr0.32Ga0.68Te2.33 with Concurrent Broken Inversion Symmetry and Ferromagnetism: A Bulk Ferrovalley Material Candidate.

The valleytronic state found in group-VI transition-metal dichalcogenides such as MoS2 has attracted immense interest since its valley degree of freedom could be used as an information carrier. However, valleytronic applications require spontaneous valley polarization. Such an electronic state is predicted to be accessible in a new ferroic family of materials, i.e., ferrovalley materials, which features the coexistence of spontaneous spin and valley polarization. Although many atomic monolayer materials with hexagonal lattices have been predicted to be ferrovalley materials, no bulk ferrovalley material candidates have been reported or proposed. Here, we show that a new non-centrosymmetric van der Waals (vdW) semiconductor Cr0.32Ga0.68Te2.33, with intrinsic ferromagnetism, is a possible candidate for bulk ferrovalley material. This material exhibits several remarkable characteristics: (i) it forms a natural heterostructure between vdW gaps, a quasi-two-dimensional (2D) semiconducting Te layer with a honeycomb lattice stacked on the 2D ferromagnetic slab comprised of the (Cr, Ga)-Te layers, and (ii) the 2D Te honeycomb lattice yields a valley-like electronic structure near the Fermi level, which, in combination with inversion symmetry breaking, ferromagnetism, and strong spin-orbit coupling contributed by heavy Te element, creates a possible bulk spin-valley locked electronic state with valley polarization as suggested by our DFT calculations. Further, this material can also be easily exfoliated to 2D atomically thin layers. Therefore, this material offers a unique platform to explore the physics of valleytronic states with spontaneous spin and valley polarization in both bulk and 2D atomic crystals.

Cysteine-Activatable Near-Infrared Fluorescent Probe for Dual-Channel Tracking Lipid Droplets and Mitochondria in Epilepsy.

Dual-channel fluorescent probes could respond to a specific target and emit different wavelengths of fluorescence before and after the response. Such probes could alleviate the influence caused by the variation of the probe concentration, excitation intensity, and so on. However, for most dual-channel fluorescent probes, the probe and fluorophore faced spectral overlap, which reduced sensitivity and accuracy. Herein, we introduced a cysteine (Cys)-responsive and near-infrared (NIR) emissive AIEgen (named TSQC) with good biocompatibility to dual-channel monitor Cys in mitochondria and lipid droplets (LDs) during cell apoptosis through wash-free fluorescence bio-imaging. TSQC can label mitochondria with bright fluorescence around 750 nm, and after reacting with Cys, the reaction product TSQ could spontaneously target LDs with emissions around 650 nm. Such spatially separated dual-channel fluorescence responses could significantly improve detection sensitivity and accuracy. Furthermore, the Cys-triggered dual-channel fluorescence imaging in LDs and mitochondria during apoptosis induced by UV light exposure, H2O2, or LPS treatment is clearly observed for the first time. Besides, we also report here that TSQC can be used to image subcellular Cys in different cell lines by measuring the fluorescence intensities of different emission channels. In particular, TSQC shows superior utility for the in vivo imaging of apoptosis in acute and chronic epilepsy mice. In brief, the newly designed NIR AIEgen TSQC can respond to Cys and separate two fluorescence signals to mitochondria and LDs, respectively, to study Cys-related apoptosis.

Engineering Sandwiched Nanochannel Aptasensor for Efficiently Screening Cancer Cells.

Cancer cells are a class of important tumor biomarkers and are closely related to tumorous progression. It is urgent to develop a sensitive and highly efficient method for the rapid and accurate detection of cancer cells. Herein, an aptamer sandwiched nanochannel electrochemical sensor was established for the highly selective determination of cancer cells. By virtue of the porous nanochannels as the filter platform and immobilized with DNA aptamers for specifically capturing the cancer cells, the nanochannel-based electrochemical sensor denotes excellent performance for MCF-7 screening, and allowing a low limit of detection of 36 cells mL-1 . The nanochannels-based sandwich structure aptasensor not only presents an efficacious and reliable approach for cancer cell detection but also provides great advantage for preventing electrode passivation in the process of biomarkers analysis.

Synthesis and Magnetic, Optical, and Electrocatalytic Properties of High-Entropy Mixed-Metal Tungsten and Molybdenum Oxides.

High-entropy oxides (HEOs) are of interest for their unique physical and chemical properties. Significant lattice distortions, strain, and tolerance for high-vacancy concentrations set HEOs apart from single-metal or mixed-metal oxides. Herein, we synthesized and characterized the structures and compositions, along with the optical, magnetic, and electrocatalytic properties, of two families of high-entropy mixed-metal tungsten and molybdenum oxides, AWO4 and B2Mo3O8, where A and B are 3d transition metals. The HEOs A6WO4 (A = Mn, Fe, Co, Ni, Cu, and Zn) and B25Mo3O8 (B = Mn, Fe, Co, Ni, and Zn), as well as all accessible single-metal AWO4 and B2Mo3O8 parent compounds, were synthesized using high-temperature solid-state methods. X-ray photoelectron spectroscopy analysis of the surfaces revealed that the HEOs largely had the metal oxidation states expected from the bulk chemical formulas, but in some cases they were different than in the parent compounds. A6WO4 exhibited antiferromagnetic (AFM) ordering with a Néel temperature of 30 K, which is less than the average of its AFM parent compounds, and had a narrow band gap of 0.24 eV, which is much lower than all of its parent compounds. B25Mo3O8 was paramagnetic, despite the existence of AFM and ferromagnetic ordering in several of its parent compounds and had no observable band gap, which is analogous to its parent compounds. Both A6WO4 and B25Mo3O8 exhibited superior catalytic activity relative to the parent compounds for the oxygen evolution reaction, the oxidation half reaction of overall water splitting, under alkaline conditions, based on the overpotential required to reach the benchmark surface area normalized current density. Consistent with literature predictions of OER durability for ternary tungsten and molybdenum oxides, A6WO4 and B25Mo3O8 also exhibited stable performance without significant dissolution during 10 h stability experiments at a constant current.

Delicate Ferromagnetism in MnBi6Te10.

Tailoring magnetic orders in topological insulators is critical to the realization of topological quantum phenomena. An outstanding challenge is to find a material where atomic defects lead to tunable magnetic orders while maintaining a nontrivial topology. Here, by combining magnetization measurements, angle-resolved photoemission spectroscopy, and transmission electron microscopy, we reveal disorder-enabled, tunable magnetic ground states in MnBi6Te10. In the ferromagnetic phase, an energy gap of 15 meV is resolved at the Dirac point on the MnBi2Te4 termination. In contrast, antiferromagnetic MnBi6Te10 exhibits gapless topological surface states on all terminations. Transmission electron microscopy and magnetization measurements reveal substantial Mn vacancies and Mn migration in ferromagnetic MnBi6Te10. We provide a conceptual framework where a cooperative interplay of these defects drives a delicate change of overall magnetic ground state energies and leads to tunable magnetic topological orders. Our work provides a clear pathway for nanoscale defect-engineering toward the realization of topological quantum phases.

Quantum Transport of the 2D Surface State in a Nonsymmorphic Semimetal.

In a topological semimetal with Dirac or Weyl points, the bulk-boundary correspondence principle predicts a gapless edge mode if the essential symmetry is still preserved at the surface. The detection of such topological surface state has been considered as the fingerprint prove for crystals with nontrivial topological bulk band. On the contrary, it has been proposed that even with symmetry broken at the surface, a new surface band can emerge in nonsymmorphic topological semimetals. The symmetry reduction at the surface lifts the bulk band degeneracies and produces an unusual "floating" surface band with trivial topology. Here, we first report quantum transport probing to ZrSiSe thin flakes and directly reveal transport signatures of this new surface state. Remarkably, though topologically trivial, such a surface band exhibits substantial two-dimensional Shubnikov-de Haas quantum oscillations with high mobility, which signifies a new protection mechanism and may open applications for quantum computing and spintronic devices.

Magnetic-Field-Induced Re-entrance of Superconductivity in Ta2PdS5 Nanostrips.

The motion of Abrikosov vortices is the dominant origin of dissipation in type II superconductors subjected to a magnetic field, which leads to a finite electrical resistance. It is generally believed that the increase in the magnetic field results in the aggravation of energy dissipation through the increase in vortex density. Here, we show a distinctive re-entrance of the dissipationless state in quasi-one-dimensional superconducting Ta2PdS5 nanostrips. Utilizing magnetotransport measurements, we unveil a prominent magnetoresistance drop with the increase in the magnetic field below the superconducting transition temperature, manifesting itself as a giant re-entrance to the superconducting phase. Time-dependent Ginzburg-Landau calculations show that this is originated from the suppression of the vortex motion by the increased energy barrier on the edges. Interestingly, both our experiments and simulations demonstrate that this giant re-entrance of superconductivity occurs only in certain geometrical regimes because of the finite size of the vortex.

An Activity-Based Fluorescent Probe for Imaging Fluctuations of Peroxynitrite (ONOO- ) in the Alzheimer's Disease Brain.

Peroxynitrite (ONOO- ) plays a critical role in Alzheimer's disease (AD). To reveal the ONOO- influx in AD brains, an activatable activity-based fluorescence probe Rd-DPA3 was designed by a structure-modulated strategy. Taking advantage of ONOO- -initiated two-step cascade reactions of a novel chemical trigger, Rd-DPA3 specifically responds to ONOO- in 0.3 mM of other reactive oxygen species (ROS) and varied proteins, and gives an intensive fluorescence enhancement (F/F0 =50). Moreover, with its mitochondria-targeting ability, Rd-DPA3 can be used to efficiently monitor the alternations of intracellular ONOO- levels in cerebral cells during oxidative stress. Significantly, due to NIR emission and good blood-brain barrier (BBB) crossing ability, Rd-DPA3 is suitable for in vivo imaging of cerebral ONOO- influx and illustrating an age-dependent accumulation of ONOO- in AD mice brains.

Highly Sensitive Near-Infrared Imaging of Peroxynitrite Fluxes in Inflammation Progress.

Inflammation is an important protection reaction in living organisms associated with many diseases. Since peroxynitrite (ONOO-) is engaged in the inflammatory processes, illustrating the key nexus between ONOO- and inflammation is significant. Due to the lack of sensitive ONOO- in vivo detection methods, the research still remains at its infancy. Herein, a highly sensitive NIR fluorescence probe DDAO-PN for in vivo detection of ONOO- in inflammation progress was reported. The probe responded to ONOO- with significant NIR fluorescence enhancement at 657 nm (84-fold) within 30 s in solution. Intracellular imaging of exogenous ONOO- with the probe demonstrated a 68-fold fluorescence increase (F/F0). Impressively, the probe can in vivo detect ONOO- fluxes in LPS-induced rear leg inflammation with a 4.0-fold fluorescence increase and LPS-induced peritonitis with an 8.0-fold fluorescence increase The remarkable fluorescence enhancement and quick response enabled real-time tracking of in vivo ONOO- with a large signal-to-noise (S/N) ratio. These results clearly denoted that DDAO-PN was able to be a NIR fluorescence probe for in vivo detection and high-fidelity imaging of ONOO- with high sensitivity and will boost the research of inflammation-related diseases.

Estimation of Heavy Metals in Tailings and Soils Using Hyperspectral Technology: A Case Study in a Tin-Polymetallic Mining Area.

Rapid assessment of heavy metal (HM) pollution in mining areas is urgently required for further remediation. Here, hyperspectral technology was used to predict HM contents of multi-media environments (tailings, surrounding soils and agricultural soils) in a mining area. The correlation between hyperspectral data and HMs was explored, then the prediction models were established by partial least squares regression (PLSR) and back propagation neural networks (BPNN). The determination coefficients (R2), root mean squared error and ratios of performance to interquartile range (RPIQ) were used to evaluate the performance of the models. Results show that: (1) both PLSR and BPNN had good prediction ability, and (2) BPNN had better generalization ability (Cu (R2 = 0.89, RPIQ = 3.05), Sn (R2 = 0.86, RPIQ = 4.91), Zn (R2 = 0.74, RPIQ = 1.44) and Pb (R2 = 0.70, RPIQ = 2.10)). In summary, this study indicates that hyperspectral technology has potential application in HM estimation and soil pollution investigation in polymetallic mining areas.

Pollution Characteristics and Risk Assessment of Potential Toxic Elements in a Tin-polymetallic Mine Area Southwest China: Environmental Implications by Multi-Medium Analysis.

A multi-medium system, involving tailing area (tailings, surrounding soils and water) and downstream agricultural area (river water, sediments and farmland soils), was conceived to evaluate the pollution status of potential toxic elements (PTEs, including Fe, Mn, Ni, Cu, Zn, As, Sn, Pb, Cr and Cd) and environmental risks in a tin-polymetallic mine area southwest China. The results indicated that tailings exhibited representative enrichment and combination characteristics of Sn, Cu, Ni, Fe, As, Pb and Cr compared to surrounding soils. Acid mine drainage (AMD) from tailings and other mining-related sources greatly affected river water and farmland soils, resulting in soil acidification and accumulation of Sn, As, Cu and Pb in paddy soils. Overall, potential ecological risks posed by tailings and river sediments, and pollution risks from Cu, As and Pb in farmland should be concerned. Therefore, effective measures should be urgently taken to prevent PTEs and AMD into surrounding environmental media.

Activatable Two-Photon Near-Infrared Fluorescent Probe Tailored toward Peroxynitrite In Vivo Imaging in Tumors.

A malignant tumor remains one of the leading causes of deaths across the world. Thus, diagnosis of tumor development with noninvasive visualizing methods is significant for tumor therapy. Herein, an activatable two-photon NIR fluorescent probe DHQ-Rd-PN for in vivo imaging of peroxynitrite in a tumor was elaborately designed. The probe demonstrated an increased NIR emission in response to peroxynitrite in vitro, which ensured that the probe detects ONOO- in cell and in vivo. Cellular imaging results disclosed that the probe was competent to detect adscititious ONOO- level change in HeLa cells, as well as endogenous ONOO- concentration in lipopolysaccharides (LPS) and IFN-γ-stimulated RAW 264.7 cells. Additionally, zebrafish in vivo imaging revealed that the probe accumulated in the pancreas and was lightened up by the addition of ONOO-. Remarkably, the probe can be harnessed to image an ONOO- production profile in xenograft 4T1 tumor mice by both one-photon and two-photon in vivo fluorescence imaging. Benefiting with the two-photon excitable properties and NIR emissive properties, the probe can be used for noninvasive in vivo imaging of ONOO- in the onset and development of tumors for the first time. This work provided a noninvasive and efficient detection method for ONOO- in a tumor, which would find more applications in tumor diagnosis and therapies.

IrO_{2} Surface Complexions Identified through Machine Learning and Surface Investigations.

A Gaussian approximation potential was trained using density-functional theory data to enable a global geometry optimization of low-index rutile IrO_{2} facets through simulated annealing. Ab initio thermodynamics identifies (101) and (111) (1×1) terminations competitive with (110) in reducing environments. Experiments on single crystals find that (101) facets dominate and exhibit the theoretically predicted (1×1) periodicity and x-ray photoelectron spectroscopy core-level shifts. The obtained structures are analogous to the complexions discussed in the context of ceramic battery materials.

Net negative contributions of free electrons to the thermal conductivity of NbSe3 nanowires.

Understanding transport mechanisms of electrons and phonons, two major energy carriers in solids, are crucial for various engineering applications. It is widely believed that more free electrons in a material should correspond to a higher thermal conductivity; however, free electrons also scatter phonons to lower the lattice thermal conductivity. The net contribution of free electrons has been rarely studied because the effects of electron-phonon (e-ph) interactions on lattice thermal conductivity have not been well investigated. Here an experimental study of e-ph scattering in quasi-one-dimensional NbSe3 nanowires is reported, taking advantage of the spontaneous free carrier concentration change during charge density wave (CDW) phase transition. Contrary to the common wisdom that more free electrons would lead to a higher thermal conductivity, results show that during the depinning process of the condensed electrons, while the released electrons enhance the electronic thermal conductivity, the overall thermal conductivity decreases due to the escalated e-ph scattering. This study discloses how competing effects of free electrons result in unexpected trends and provides solid experimental data to dissect the contribution of e-ph scattering on lattice thermal conductivity. Lastly, an active thermal switch design is demonstrated based on tuning electron concentration through electric field.

Distinct Signatures of Electron-Phonon Coupling Observed in the Lattice Thermal Conductivity of NbSe3 Nanowires.

The last two decades have seen tremendous progress in quantitative understanding of several major phonon scattering mechanisms (phonon-phonon, phonon-boundary, phonon-defects), as they are the determinant factors in lattice thermal transport, which is critical for the proper functioning of various electronic and energy conversion devices. However, the roles of another major scattering mechanism, electron-phonon (e-ph) interactions, remain elusive. This is largely due to the lack of solid experimental evidence for the effects of e-ph scattering in the lattice thermal conductivity for the material systems studied thus far. Here we show distinct signatures in the lattice thermal conductivity observed below the charge density wave transition temperatures in NbSe3 nanowires, which cannot be recaptured without considering e-ph scattering. Our findings can serve as the cornerstone for quantitative understanding of the e-ph scattering effects on lattice thermal transport in many technologically important materials.