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Layer-stacking domain wall in bilayer graphene is one type of topological defects that can greatly affect the electronic properties of bilayer graphene and therefore lead to nontrivial transport behaviors. An outstanding question on the layer stacking domain wall is how the electrons hop between two adjacent stacking domains. Here we report the first experimental observation of electronic transport across bilayer graphene domain walls by combining near-field infrared nanoscopy and scanning voltage microscopy techniques. We observe markedly different electron transport behaviors across the tensile- and shear-type domain walls. The tensile-type domain wall is highly reflective of low-energy incident electrons, but becomes more transparent when the electron density and the Fermi energy are increased by electrostatic gating. In contrast, the shear-type domain wall is always highly transparent at different gate voltages. Such soliton-dependent electronic transport can open up new routes to engineer novel nanoelectronic devices based on layer-stacking domain walls in bilayer graphene.

Studies of two-dimensional electron systems in a strong magnetic field revealed the quantum Hall effect1, a topological state of matter featuring a finite Chern number C and chiral edge states2,3. Haldane4 later theorized that Chern insulators with integer quantum Hall effects could appear in lattice models with complex hopping parameters even at zero magnetic field. The ABC-trilayer graphene/hexagonal boron nitride (ABC-TLG/hBN) moiré superlattice provides an attractive platform with which to explore Chern insulators because it features nearly flat moiré minibands with a valley-dependent, electrically tunable Chern number5,6. Here we report the experimental observation of a correlated Chern insulator in an ABC-TLG/hBN moiré superlattice. We show that reversing the direction of the applied vertical electric field switches the moiré minibands of ABC-TLG/hBN between zero and finite Chern numbers, as revealed by large changes in magneto-transport behaviour. For topological hole minibands tuned to have a finite Chern number, we focus on quarter filling, corresponding to one hole per moiré unit cell. The Hall resistance is well quantized at h/2e2 (where h is Planck's constant and e is the charge on the electron), which implies C = 2, for a magnetic field exceeding 0.4 tesla. The correlated Chern insulator is ferromagnetic, exhibiting substantial magnetic hysteresis and a large anomalous Hall signal at zero magnetic field. Our discovery of a C = 2 Chern insulator at zero magnetic field should open up opportunities for discovering correlated topological states, possibly with topological excitations7, in nearly flat and topologically nontrivial moiré minibands.

A key feature of two-dimensional materials is that the sign and concentration of their carriers can be externally controlled with techniques such as electrostatic gating. However, conventional electrostatic gating has limitations, including a maximum carrier density set by the dielectric breakdown, and ionic liquid gating and direct chemical doping also suffer from drawbacks. Here, we show that an electron-beam-induced doping technique can be used to reversibly write high-resolution doping patterns in hexagonal boron nitride-encapsulated graphene and molybdenum disulfide (MoS2) van der Waals heterostructures. The doped MoS2 device exhibits an order of magnitude decrease of subthreshold swing compared with the device before doping, whereas the doped graphene devices demonstrate a previously inaccessible regime of high carrier concentration and high mobility, even at room temperature. We also show that the approach can be used to write high-quality p–n junctions and nanoscale doping patterns, illustrating that the technique can create nanoscale circuitry in van der Waals heterostructures.

Changes in labile carbon (LC) pools and microbial communities are the primary factors controlling soil heterotrophic respiration (Rh ) in warming experiments. Warming is expected to initially increase Rh but studies show this increase may not be continuous or sustained. Specifically, LC and soil microbiome have been shown to contribute to the effect of extended warming on Rh . However, their relative contribution is unclear and this gap in knowledge causes considerable uncertainty in the prediction of carbon cycle feedbacks to climate change. In this study, we used a two-step incubation approach to reveal the relative contribution of LC limitation and soil microbial community responses in attenuating the effect that extended warming has on Rh . Soil samples from three Tibetan ecosystems-an alpine meadow (AM), alpine steppe (AS), and desert steppe (DS)-were exposed to a temperature gradient of 5-25°C. After an initial incubation period, soils were processed in one of two methods: (a) soils were sterilized then inoculated with parent soil microbes to assess the LC limitation effects, while controlling for microbial community responses; or (b) soil microbes from the incubations were used to inoculate sterilized parent soils to assess the microbial community effects, while controlling for LC limitation. We found both LC limitation and microbial community responses led to significant declines in Rh by 37% and 30%, respectively, but their relative contributions were ecosystem specific. LC limitation alone caused a greater Rh decrease for DS soils than AMs or ASs. Our study demonstrates that soil carbon loss due to Rh in Tibetan alpine soils-especially in copiotrophic soils-will be weakened by microbial community responses under short-term warming.

Understanding the mechanism of high-transition-temperature (high-Tc) superconductivity is a central problem in condensed matter physics. It is often speculated that high-Tc superconductivity arises in a doped Mott insulator1 as described by the Hubbard model2-4. An exact solution of the Hubbard model, however, is extremely challenging owing to the strong electron-electron correlation in Mott insulators. Therefore, it is highly desirable to study a tunable Hubbard system, in which systematic investigations of the unconventional superconductivity and its evolution with the Hubbard parameters can deepen our understanding of the Hubbard model. Here we report signatures of tunable superconductivity in an ABC-trilayer graphene (TLG) and hexagonal boron nitride (hBN) moiré superlattice. Unlike in 'magic angle' twisted bilayer graphene, theoretical calculations show that under a vertical displacement field, the ABC-TLG/hBN heterostructure features an isolated flat valence miniband associated with a Hubbard model on a triangular superlattice5,6 where the bandwidth can be tuned continuously with the vertical displacement field. Upon applying such a displacement field we find experimentally that the ABC-TLG/hBN superlattice displays Mott insulating states below 20 kelvin at one-quarter and one-half fillings of the states, corresponding to one and two holes per unit cell, respectively. Upon further cooling, signatures of superconductivity ('domes') emerge below 1 kelvin for the electron- and hole-doped sides of the one-quarter-filling Mott state. The electronic behaviour in the ABC-TLG/hBN superlattice is expected to depend sensitively on the interplay between the electron-electron interaction and the miniband bandwidth. By varying the vertical displacement field, we demonstrate transitions from the candidate superconductor to Mott insulator and metallic phases. Our study shows that ABC-TLG/hBN heterostructures offer attractive model systems in which to explore rich correlated behaviour emerging in the tunable triangular Hubbard model.

Strain plays an important role in condensed matter physics and materials science because it can strongly modify the mechanical, electrical, and optical properties of a material and even induce a structural phase transition. Strain effects are especially interesting in atomically thin two-dimensional (2D) materials, where unusually large strain can be achieved without breaking them. Measuring the strain distribution in 2D materials at the nanometer scale is therefore greatly important but is extremely challenging experimentally. Here, we use near-field infrared nanoscopy to demonstrate phonon polariton-assisted mapping and quantitative analysis of strain in atomically thin polar crystals of hexagonal boron nitride (hBN) at the nanoscale. A local strain as low as 0.01% can be detected using this method with ∼20 nm spatial resolution. Such ultrasensitive nanoscale strain imaging and analysis technique opens up opportunities for exploring unique local strain structures and strain-related physics in 2D materials. In addition, experimental evidence for local strain-induced phonon polariton reflection is also provided, which offers a new approach to manipulate light at deep subwavelength scales for nanophotonic devices.

The Mott insulator is a central concept in strongly correlated physics and manifests when the repulsive Coulomb interaction between electrons dominates over their kinetic energy1,2. Doping additional carriers into a Mott insulator can give rise to other correlated phenomena such as unusual magnetism and even high-temperature superconductivity2,3. A tunable Mott insulator, where the competition between the Coulomb interaction and the kinetic energy can be varied in situ, can provide an invaluable model system for the study of Mott physics. Here we report the possible realization of such a tunable Mott insulator in a trilayer graphene heterostructure with a moiré superlattice. The combination of the cubic energy dispersion in ABC-stacked trilayer graphene4–8 and the narrow electronic minibands induced by the moiré potential9–15 leads to the observation of insulating states at the predicted band fillings for the Mott insulator. Moreover, the insulating states in the heterostructure can be tuned: the bandgap can be modulated by a vertical electrical field, and at the same time the electron doping can be modified by a gate to fill the band from one insulating state to another. This opens up exciting opportunities to explore strongly correlated phenomena in two-dimensional moiré superlattice heterostructures.

Fluopimomide is a novel acid amide fungicide registered for the control of many plant pathogens. In the present study, the effects of soil-treated fluopimomide on soil micro biomass, disease incidence, plant growth, soil enzyme activity, and marketable yield of tomato (Solanum lycopersicum L.) were investigated via field trial. In addition, the application prospect in China was also evaluated. In the experiment, five treatments with three replications and a randomized complete block design were followed. The treatments were: furrow application of fluopimomide (25% suspension concentrate, SC) at the dosage of 375, 750, and 1,500 g ha−1, which was recommended, double recommended, and quadruple recommended dosages, respectively. Besides, common control fungicide fluopicolide (5% SC) furrow was applied at recommended application dosages of 750 mL ha−1, and a non-treated control was also undertaken. Results indicated that fluopimomide exhibited no effects on the amount of soil bacteria and actinomycetes, and its inhibition effect on fungi amount could be recovered at 60 days after treatment (DAT). With the recommended application dosage, fluopimomide could efficiently reduce the number of plant pathogens in soil by 79.56–85.80%, significantly reduce the disease incidences in tomato plants by 80.00–88.24%, and improve plant height by 13.25–24.05% and marketable yield by 16.88%. Furthermore, soil enzymes exhibited a complex response to fluopimomide, and AOB and nifH gene copy numbers were increased by the double and quadruple recommended dosage of fluopimomide. Based on the above results, fluopimomide could be recommended as an efficient fungicide for the tomato field.

With mine drainage and activities, the hydrogeochemical environments has greatly changed in Kongjiagou coalmine, Sichuan Province, southwest China. This study aimed to summarize an ideal model of coalmine hydrogeochemical zonation and evolution. In total, 24 groundwater samples from different depth were collected to analyze their components, with the combination of methods such as ion sources, normalization index, ions ratios, cation exchange and inverse modeling. The hydrogeochemical formation main factor was water–rock reactions and more weathering by sulfuric acid. Dissolution and pyrite oxidation were the main sources of , whereas carbonate weathering was the dominant source of . The vertical extent could be distinguished to three zones by mean and standard deviation of burial depth. The normalization index, ions ratios, cation exchange and water types exhibited clear vertical zonation. In shallow groundwater, dissolution led to a Ca- type water and overall stable concentrations of ions. Redox reactions in the middle region have caused significant increases in the total dissolved solids (TDS) and and a considerable reduction in pH; hence, Ca + Mg-SO4 + HCO3 became the dominant type. Re-dissolution and cation exchange played important roles at depth and caused the pH and TDS to increase slowly. The , Ca2+, and Mg2+ concentrations increased rapidly, whereas the concentration remained basically unchanged, and the water type was either Ca + Mg-HCO3 + SO4 or Na-HCO3 + SO4. This study will be of great significance to coalmine safety production and water environments protection. HIGHLIGHTS Distinguished vertical zonation based on mean and standard deviation of burial depth.; Introduced ions normalization index for hydrogeochemical analysis.; PHREEQC was used to calculate the amount transferred from shallow to deep.; The main reactions from shallow to deep were dissolution, redox, re-dissolution and cation exchange.; Summarized an ideal vertical zoning model and mechanism of coal mine hydrogeochemically.;