Stripe phases, in which the rotational symmetry of charge density is spontaneously broken, occur in many strongly correlated systems with competing interactions1–11. However, identifying and studying ...such stripe phases remains challenging. Here we uncover stripe phases in WSe2/WS2 moiré superlattices by combining optical anisotropy and electronic compressibility measurements. We find strong electronic anisotropy over a large doping range peaked at 1/2 filling of the moiré superlattice. The 1/2 state is incompressible and assigned to an insulating stripe crystal phase. Wide-field imaging reveals domain configurations with a preferential alignment along the high-symmetry axes of the moiré superlattice. Away from 1/2 filling, we observe additional stripe crystals at commensurate filling 1/4, 2/5 and 3/5, and compressible electronic liquid crystal states at incommensurate fillings. Our results demonstrate that two-dimensional semiconductor moiré superlattices are a highly tunable platform from which to study the stripe phases and their interplay with other symmetry breaking ground states.Optical anisotropy and electronic compressibility measurements are used to uncover stripe phases, where the rotational symmetry of charge density is spontaneously broken, in a two-dimensional semiconductor moiré superlattice.
Strong magnetization fluctuations are expected near the thermodynamic critical point of a continuous magnetic phase transition. Such critical fluctuations are highly correlated and in principle can ...occur at any time and length scales
; they govern critical phenomena and potentially can drive new phases
. Although critical phenomena in magnetic materials have been studied using neutron scattering, magnetic a.c. susceptibility and other techniques
, direct real-time imaging of critical magnetization fluctuations remains elusive. Here we develop a fast and sensitive magneto-optical imaging microscope to achieve wide-field, real-time monitoring of critical magnetization fluctuations in single-layer ferromagnetic insulator CrBr
. We track the critical phenomena directly from the fluctuation correlations and observe both slowing-down dynamics and enhanced correlation length. Through real-time feedback control of the critical fluctuations, we further achieve switching of magnetic states solely by electrostatic gating. The ability to directly image and control critical fluctuations in 2D magnets opens up exciting opportunities to explore critical phenomena and develop applications in nanoscale engines and information science.
We conduct a comprehensive study of three different magnetic semiconductors, CrI₃, CrBr₃, and CrCl₃, by incorporating both few-layer and bilayer samples in van der Waals tunnel junctions. We find ...that the interlayer magnetic ordering, exchange gap, magnetic anisotropy, and magnon excitations evolve systematically with changing halogen atom. By fitting to a spin wave theory that accounts for nearest-neighbor exchange interactions, we are able to further determine a simple spin Hamiltonian describing all three systems. These results extend the 2D magnetism platform to Ising, Heisenberg, and XY spin classes in a single material family. Using magneto-optical measurements, we additionally demonstrate that ferromagnetism can be stabilized down to monolayer in more isotropic CrBr₃, with transition temperature still close to that of the bulk.
Many concerns have been raised about ecological and environmental risks from the disposal of red mud (RM) in the aluminium industry. For a long time a suitable use for RM, due to the huge amount ...produced, has been needed. This study, for the first time, applies RM as an efficient electrochemical catalyst in the emerging nitrate-to-ammonia reduction reaction (NARR) based on renewable energy, in which the produced green ammonia can supply energy for rechargeable ammonia energy storage (RAES). The performance of RM stands out among many other synthetic catalysts in the NARR as well as further combination with photovoltaic technology. Specifically, it exhibits a superior faradaic efficiency toward NH
3
of 92.8% and an NH
3
formation rate of 0.16 mmol cm
−2
h
−1
under −0.73 V (
vs
. reversible hydrogen electrode) in a neutral phosphate buffer solution with 1.0 M NO
3
−
. The energy efficiency toward NH
3
is over 30% in a two-electrode system, and that of the solar-to-NH
3
conversion is 2.09% at a light intensity of 0.06 W cm
−2
based on a commercial poly-Si photovoltaic cell. The results promise a low-cost RM catalyst for the NARR sustainable route, realizing RM recycling and zero-carbon ammonia-energy production.
A sustainable red mud disposal solution is proposed based on the emerging electrocatalytic nitrate-to-ammonia reduction reaction, exhibiting outstanding performance and efficient energy conversion compared to many other synthetic catalysts.
Chlorophyll-a (Chl-a) is an important characterized parameter of lakes. Monitoring it accurately through remote sensing is thus of great significance for early warnings of water eutrophication. ...Sentinel Multispectral Imager (MSI) images from May to September between 2020 and 2021 were used along with in-situ measurements to estimate Chl-a in Lake Chagan, which is located in Jilin Province, Northeast China. In this study, the extreme gradient boosting (XGBoost) and Random Forest (RF) models, which had similar performances, were generated by six single bands and six band combinations. The RF model was then selected based on the assessments (R2 = 0.79, RMSE = 2.51 μg L−1, MAPE = 9.86%), since its learning of the input features in the model conformed to the bio-optical properties of Case 2 waters. The study considered Chl-a concentrations in Lake Chagan as a seasonal pattern according to the K-Nearest-Neighbors (KNN) classification. The RF model also showed relatively stable performance for three seasons (spring, summer and autumn) and it was applied to map Chl-a in the whole lake. The research presents a more reliable machine learning (ML) model with higher precision than previous empirical models, as shown by the effects of the input features linked with the biological mechanisms of Chl-a. Its robustness was revealed by the temporal and spatial distributions of Chl-a concentrations, which were consistent with in-situ measurements in the map. This research was capable of revealing the current ecological situation in Lake Chagan and can serve as a reference in remote sensing of inland lakes.
Lead (II) is regarded as one of the most hazardous heavy metals, and lead contamination has a serious impact on food chains, human health, and the environment. Herein, a colorimetric aptasensor based ...on the graphene/Fe3O4-AuNPs composites with enhanced peroxidase-like activity has been developed to monitor lead ions (Pb2+). In short, graphene/Fe3O4-AuNPs were fabricated and acted as an enzyme mimetic, so the color change could be observed by chromogenic reaction. The aptamer of Pb2+ was decorated on the surface of the amine magnetic beads by streptavidin–biotin interaction, and the complementary strands of the aptamer and target Pb2+ competed for the binding Pb2+ aptamer. In the presence of Pb2+, aptamers bonded the metal ions and were removed from the system by magnetic separation; the free cDNA was adsorbed onto the surface of the graphene/Fe3O4-AuNPs composites, thus inhibiting the catalytic activity and the color reaction. The absorbance of the reaction solution at 652 nm had a clear linear correlation with the Pb2+ concentration in the range of 1–300 ng/mL, and the limit of detection was 0.63 ng/mL. This assay is simple and convenient in operation, has good selectivity, and has been used to test tap water samples, which proves that it is capable for the routine monitoring of Pb2+.
The design and performance of a novel octave-bandwidth highly-directive half Maxwell fish-eye (HMFE) lens antenna are presented in superextended C band. The three-dimensional (3D) HMFE lens is ...implemented by gradient-refractive-index (GRIN) metamaterials and launched by an omnidirectional planar microstrip trapezoid printed monopole from the perspective of high integration, light weight and low profile. A new approach is proposed to design the GRIN metamaterial element in terms of a deep subwavelength feature by incorporating fractal geometry. Numerical and experimental results coincide well, showing that the lens enables a considerable gain enhancement of the monopole near 10 dB across a frequency range of 3 to 7.5 GHz while without significantly affecting the cross-polarization patterns and impedance matching. The near-field free-space measurement is also performed in an octave to afford a physical insight into the high gain, which is attributable to the accurate conversion of quasi-spherical waves to plane waves. Moreover, the truncation and homogenization effects of the lens on the antenna directivity are investigated to illustrate the fundamental mechanisms and afford the design guidelines.
An in-depth exploration of fractional vegetation coverage (FVC) changes and driving mechanisms in the Yangtze River Delta (YRD) is crucial for maintaining regional ecological health and achieving ...sustainable development. We therefore calculate FVC in the YRD from 2012 to 2021 based on MODIS NDVI data, and analyze its spatiotemporal evolution. Multiple regression residual analysis and geographic detector model were used along with various auxiliary data to further explore its driving mechanisms in a hierarchical manner. Finally, the Hurst index was used to forecast future trends in FVC. The results show that: 1) Significant changes in FVC occurred around 2016, rapidly declining at a rate of 8.9×10 -3 a -1 from 2012 to 2016, followed by fluctuating growth at a rate of 5.2×10 -3 a -1 thereafter. 2) Although the overall development of FVC in the YRD tends toward stability, the fluctuation was pronounced in the Taihu Lake Basin. Improvement areas were mainly concentrated on both sides of the Yangtze River in the central part of the YRD and in the southern mountainous region. Degraded areas were concentrated in cities north of the Huai River. 3) Dynamic changes in FVC were primarily driven by a combination of climate and human activities, whereas spatial heterogeneity was mainly driven by factors such as elevation, slope, and landform type. The improvement in the explanatory power of anthropogenic factors for spatial heterogeneity when combined with natural factors was significant.
Herein, in situ water reflectance and TSM data obtained from several experiments on the Nanyi Lake from 2018 to 2022 and the Sentinel-3 Ocean and Land Colour Instrument (OLCI) satellite ...synchronization data were used to compare four atmospheric correction methods (FLAASH, 6S, ACOLITE, and C2RCC) and construct an empirical model for TSM inversion in the Nanyi Lake to analyze the spatial and temporal changes in the water quality in the Nanyi Lake from 2018 to 2023. On the Sentinel-3 OLCI data, the C2RCC algorithm showed the highest accuracy and overall performance stability (RMSE: 0.0014-0.0051 Sr −1 , MAPE: 18.44%-68.47%, and BIAS: from −3.68% to 23.63%). The highest correlation was observed between the three-band ratio (B9 + B18)/B10 and the in situ TSM; the TSM inversion model constructed based on this inversion factor showed the best accuracy for the Nanyi Lake (R 2 : 0.76, RMSE: 5.01 mg/L, and MAPE: 28.46%). The spatial and temporal changes in TSM in the Nanyi Lake exhibited significant regularity. Specifically, the TSM was higher in 2018-2019, significantly decreased in 2020, and stabilized in 2021-2023. Owing to the effects of human activities, precipitation, and illumination, seasonal variation in the TSM in the Nanyi Lake was detected, with TSM decreasing in the following order: summer > autumn > spring > winter. Concerning spatial variations, high TSM was observed in the northwest, northeast, and southeast of the Nanyi Lake reclamation area and its surrounding lake area. River confluence and human activities affected the area, leading to significant fluctuations in TSM in 2018-2023.
Lake ecosystem eutrophication is a crucial water quality issue that can be efficiently monitored with remote sensing. GF-6 WFV with a high spatial and temporal resolution provides a comprehensive ...record of the dynamic changes in water quality parameters in a lake. In this study, based on GF-6 WFV images and the field sampling data of Xingkai Lake from 2020 to 2021, the accuracy of three machine learning models (RF: random forest; SVR: support vector regression; and BPNN: back propagation neural network) was compared by considering 11 combinations of surface reflectance in different wavebands as input variables for machine learning. We mapped the spatiotemporal variations of Chl-a concentrations in Xingkai Lake from 20192021 and integrated machine learning algorithms to demonstrate that RF obtained a better degree of derived-fitting (Calibration: N = 82, RMSE = 0.82 μg/L, MAE = 0.57 μg/L, slope = 0.94, and R2 = 0.98; Validation: N = 40, RMSE = 2.12 μg/L, MAE = 1.58 μg/L, slope = 0.91, R2 = 0.89, and RPD = 2.98). The interannual variation from 2019 to 2021 showed that the Chl-a concentration in Xingkai Lake was low from June to July, while maximum values were observed from October to November, thus showing significant seasonal differences. Spatial distribution showed that Chl-a concentrations were higher in Xiao Xingkai Lake than in Da Xingkai Lake. Nutrient inputs (N, P) and other environmental factors such as high temperature could have an impact on the spatial and temporal distribution characteristics of Chl-a, therefore, combining GF-6 WFV satellite images with RF could realize large-scale monitoring and be more effective. Our results showed that remote-sensing-based machine learning algorithms provided an effective method to monitor lake eutrophication as well as technical support and methodological reference for inland lake water quality parameter inversion.
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