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Quantum geometry - the geometry of electron Bloch wavefunctions - is central to modern condensed matter physics. Due to the quantum nature, quantum geometry has two parts, the real part quantum metric and the imaginary part Berry curvature. The studies of Berry curvature have led to countless breakthroughs, ranging from the quantum Hall effect in 2DEGs to the anomalous Hall effect (AHE) in ferromagnets. However, in contrast to Berry curvature, the quantum metric has rarely been explored. Here, we report a new nonlinear Hall effect induced by quantum metric by interfacing even-layered MnBi2Te4 (a PT-symmetric antiferromagnet (AFM)) with black phosphorus. This novel nonlinear Hall effect switches direction upon reversing the AFM spins and exhibits distinct scaling that suggests a non-dissipative nature. Like the AHE brought Berry curvature under the spotlight, our results open the door to discovering quantum metric responses. Moreover, we demonstrate that the AFM can harvest wireless electromagnetic energy via the new nonlinear Hall effect, therefore enabling intriguing applications that bridges nonlinear electronics with AFM spintronics., Comment: 19 pages, 4 figures and a Supplementary Materials with 66 pages, 4 figures and 3 tables. Originally submitted to Science on Oct. 5, 2022

Electronic ferroelectricity represents a new paradigm where spontaneous symmetry breaking driven by electronic correlations, in contrast to traditional lattice-driven ferroelectricity, leads to the formation of electric dipoles. Despite the potential application advantages arising from its electronic nature, switchable electronic ferroelectricity remains exceedingly rare. Here, we report the discovery of an electronic ratchet effect that manifests itself as switchable electronic ferroelectricity in a layer-contrasting graphene-boron nitride moir\'e heterostructure. Our engineered layer-asymmetric moir\'e potential landscapes result in layer-polarized localized and itinerant electronic subsystems. At particular fillings of the localized subsystem, we find a ratcheting injection of itinerant carriers in a non-volatile manner, leading to a highly unusual ferroelectric response. Strikingly, the remnant polarization can be stabilized at multiple (quasi-continuous) states with behavior markedly distinct from known ferroelectrics. Our experimental observations, simulations, and theoretical analysis suggest that dipolar excitons are the driving force and elementary ferroelectric units in our system. This signifies a new type of electronic ferroelectricity where the formation of dipolar excitons with aligned moments generates a macroscopic polarization and leads to an electronically-driven ferroelectric response, which we term excitonic ferroelectricity. Such new ferroelectrics, driven by quantum objects like dipolar excitons, could pave the way to innovative quantum analog memory and synaptic devices.

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Nonlinear optical responses of quantum materials have recently undergone dramatic developments to unveil nontrivial geometry and topology. A remarkable example is the quantized longitudinal circular photogalvanic effect (CPGE) associated with the Chern number of Weyl fermions, while the physics of transverse CPGE in Weyl semimetals remains exclusive. Here, we show that the transverse CPGE of Lorentz invariant Weyl fermions is forced to be zero. We find that the transverse photocurrents of Weyl fermions are associated not only with the Chern numbers but also with the degree of Lorentz-symmetry breaking in condensed matter systems. Based on the generic two-band model analysis, we provide a new powerful equation to calculate the transverse CPGE based on the tilting and warping terms of Weyl fermions. Our results are more capable in designing large transverse CPGE of Weyl semimetals in experiments and are applied to more than tens of Weyl materials to estimate their photocurrents. Our method paves the way to study the CPGE of massless or massive quasiparticles to design next-generation quantum optoelectronics.

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Quantum geometry - the geometry of electron Bloch wavefunctions - is central to modern condensed matter physics. Due to the quantum nature, quantum geometry has two parts, the real part quantum metric and the imaginary part Berry curvature. The studies of Berry curvature have led to countless breakthroughs, ranging from the quantum Hall effect in 2DEGs to the anomalous Hall effect (AHE) in ferromagnets. However, in contrast to Berry curvature, the quantum metric has rarely been explored. Here, we report a new nonlinear Hall effect induced by quantum metric by interfacing even-layered MnBi2Te4 (a PT-symmetric antiferromagnet (AFM)) with black phosphorus. This novel nonlinear Hall effect switches direction upon reversing the AFM spins and exhibits distinct scaling that suggests a non-dissipative nature. Like the AHE brought Berry curvature under the spotlight, our results open the door to discovering quantum metric responses. Moreover, we demonstrate that the AFM can harvest wireless electromagnetic energy via the new nonlinear Hall effect, therefore enabling intriguing applications that bridges nonlinear electronics with AFM spintronics., Just appeared in Science. Originally submitted to Science on Oct. 5, 2022

Supplementary Material 1

Electronic ferroelectricity represents a new paradigm where spontaneous symmetry breaking driven by electronic correlations, in contrast to traditional lattice-driven ferroelectricity, leads to the formation of electric dipoles. Despite the potential application advantages arising from its electronic nature, switchable electronic ferroelectricity remains exceedingly rare. Here, we report the discovery of an electronic ratchet effect that manifests itself as switchable electronic ferroelectricity in a layer-contrasting graphene-boron nitride moiré heterostructure. Our engineered layer-asymmetric moiré potential landscapes result in layer-polarized localized and itinerant electronic subsystems. At particular fillings of the localized subsystem, we find a ratcheting injection of itinerant carriers in a non-volatile manner, leading to a highly unusual ferroelectric response. Strikingly, the remnant polarization can be stabilized at multiple (quasi-continuous) states with behavior markedly distinct from known ferroelectrics. Our experimental observations, simulations, and theoretical analysis suggest that dipolar excitons are the driving force and elementary ferroelectric units in our system. This signifies a new type of electronic ferroelectricity where the formation of dipolar excitons with aligned moments generates a macroscopic polarization and leads to an electronically-driven ferroelectric response, which we term excitonic ferroelectricity. Such new ferroelectrics, driven by quantum objects like dipolar excitons, could pave the way to innovative quantum analog memory and synaptic devices.

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The photoexcitation life-cycle from incident photon (and creation of photoexcited electron hole pair) to ultimate extraction of electrical current is a complex multi-physics process spanning across a range of spatio-temporal scales of quantum materials. While often viewed through a device-technology lens, photocurrent is a key observable of the life-cycle that is sensitive to a myriad of physical processes across these scales. As a result, photocurrent is emerging as a versatile probe of electronic states, Bloch band quantum geometry, quantum kinetic processes, and device characteristics of quantum materials. This review outlines the key multi-physics principles of photocurrent diagnostics. In particular, we describe how the fundamental link between light-matter interaction and quantum geometry renders photocurrent a wavefunction-sensitive probe capable of resolving bandstructure and characterizing topological materials. We further highlight the sensitivity of the photoexcitation life-cycle to relaxational processes which in turn enables photocurrent to disentangle distinct types of carrier scattering that can range from femtosecond to nanosecond timescales. We survey the intrinsically nonlocal character of photocurrent collection that allows new types remote sensing protocols and photocurrent nanoscopy. These distinctive features underscore photocurrent diagnostics as a novel multi-physics probe for a growing class of quantum materials with properties governed by physics spanning multiple spatio-temporal scales., original submitted version

Spinal cord injury refers to damage to the spinal cord due to trauma, disease, or degeneration; and the number of new cases is increasing yearly. Significant cellular changes are known to occur in the area of spinal cord injury. However, changes in cellular composition, trajectory of cell development, and intercellular communication in the injured area remain unclear. Here, we used single-cell RNA sequencing to evaluate almost all the cell types that constitute the site of spinal cord injury in rats. In addition to mapping the cells of the injured area, we screened the expression of immune autophagy-related factors in cells and identified signaling pathways by the measuring the expression of the receptor−ligand pairs to regulate specific cell interactions during autophagy after spinal cord injury. Our data set is a valuable resource that provides new insights into the pathobiology of spinal cord injury and other traumatic diseases of the central nervous system.

Supplemental Material, sj-pdf-1-ang-10.1177_00033197221082712 for Long-Term Blood Pressure Exposure From Childhood and Early Vascular Aging in Midlife: A 30-Year Prospective Cohort Study by Yu Yan, Yu Cao, Qiong Ma, Keke Wang, Yueyuan Liao, Yue Sun, Chen Chen, Jiawen Hu, Wenling Zheng, Chao Chu, Yang Wang, and Jianjun Mu in Angiology

High quality graphene on a Cu foil was synthesized by atmospheric pressure chemical vapor deposition. The morphology and microstructure of specimens were characterized by optical microscopy, scanning electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy, ultraviolet-visible spectroscopy and X-ray photoelectron spectroscopy. The corrosion resistance of specimens was tested by potentiodynamic polarization and electrochemical impedance spectroscopy. Results show that monolayer and high quality tri-layer graphene are synthesized at 1 000 °C for 5 and 15 min depositions, respectively. The monolayer graphene cannot protect Cu efficiently from oxidation at 300 °C in air and from electrochemical corrosion in a 0.1 mol/L NaCl solution due to its abundant defects and grain boundaries. The tri-layer graphene effectively increases the oxidation resistance and the electrochemical corrosion resistance. The protective performance of tri-layer graphene for a Cu foil is significantly better than that of monolayer graphene.

Qiong Ma,1 Xi Zhao,1 Anhua Shi,1 Junzi Wu1,2 1The Key Laboratory of Microcosmic Syndrome Differentiation, Education Department of Yunnan, Yunnan University of Chinese Medicine, Kunming, Yunnan 650500, People’s Republic of China; 2Department of Medical Biology, College of Basic Medicine, Yunnan University of Chinese Medicine, Kunming, Yunnan 650500, People’s Republic of ChinaCorrespondence: Junzi Wu; Anhua ShiYunnan University of Chinese Medicine, No. 1076, Yuhua Road, Chenggong District, Kunming, Yunnan 650500, People’s Republic of ChinaTel/Fax +86 187 8855 7524Email beached@126.com; 2697349858@qq.comAbstract: The glucose-sensitive self-adjusting drug delivery system simulates the physiological model of the human pancreas-secreting insulin and then precisely regulates the release of hypoglycemic drugs and controls the blood sugar. Thus, it has good application prospects in the treatment of diabetes. Presently, there are three glucose-sensitive drug systems: phenylboronic acid (PBA) and its derivatives, concanavalin A (Con A), and glucose oxidase (GOD). Among these, the glucose-sensitive polymer carrier based on PBA has the advantages of better stability, long-term storage, and reversible glucose response, and the loading of insulin in it can achieve the controlled release of drugs in the human environment. Therefore, it has become a research hotspot in recent years and has been developed very rapidly. In order to further carry out a follow-up study, we focused on the development process, performance, and application of PBA and its derivatives-based glucose-sensitive polymer drug carriers, and the prospects for the development of this field.Keywords: phenylboronic acid, glucose sensitive, diabetes

Additional file 1: Figure S1. Nanoparticle swelling images under TEM after 1(a), 4(b), 10(c), 40(d)days. Figure S2. CD spectra of the insulin released from NPs and standard insulin. Table S1. Comparison with other systems. Table S2. The Mw and Mn and PDI of the p(AAPBA-b-PTE). Table S3. Ritger–Peppas results of p(AAPBA-b-PTE)2 NPs.

Additional file 1.: Table S1. ECG parameters of participants categorized by LVH status (n=1515). Table S2. The collinearity diagnosis analysis between variables (n=1515). Table S3. Association between various characteristics and the risk of LVH by multiple logistic regression analysis in normotensive subjects (n=1344).

Youhua Yuan, 1,* Junjie Wang, 2,* Zonghui Yao, 1,* Bing Ma, 1 Yi Li, 1 Wenjuan Yan, 1 Shanmei Wang, 1 Qiong Ma, 1 Jiangfeng Zhang, 1 Junhong Xu, 1 Li Li, 1 Yuming Wang, 1 Enguo Fan 1 1Department of Clinical Microbiology, Henan Provincial People’s Hospital, People’s Hospital of Zhengzhou University, and People’s Hospital of Henan University, Zhengzhou, Henan 450003, People’s Republic of China; 2Clinical Laboratory, Luyi Zhenyuan Hospital, Zhoukou, Henan 477200, People’s Republic of China*These authors contributed equally to this workCorrespondence: Enguo Fan; Yuming WangDepartment of Clinical Microbiology Henan Provincial People’s Hospital, People’s Hospital of Zhengzhou University, and People’s Hospital of Henan University, Weiwu Road 5, Zhengzhou, Henan 450003, People’s Republic of ChinaTel +8637165580484Fax +8637187160318Email enguofan@126.com; henanyuming@sina.comPurpose: The incidence of carbapenem-resistant Klebsiella pneumoniae (CRKP) bloodstream infections (BSIs) is increasing globally; however, little has been reported on the risk factors and outcomes of CRKP BSIs in central China. This study aimed to determine the clinical risk factors for CRKP BSIs and the outcomes of CRKP BSIs.Patients and Methods: We performed a case-control study of 239 patients with K. pneumoniae BSIs who were treated at Henan Provincial People’s Hospital between July 2017 and July 2018. The cases (n=98, 41%) had CRKP BSIs, and the controls (n=141, 59%) had non-carbapenem-resistant K. pneumoniae (non-CRKP) BSIs. Antimicrobial sensitivity was determined using automated broth microdilution and an agar disk diffusion method. Data were obtained from clinical and laboratory records. Multivariate logistic regression and Pearson chi-square tests were used to identify clinical factors and outcomes associated with carbapenem resistance.Results: Risk factors for carbapenem resistance included recent carbapenem use (odds ratio [OR]: 9.98, 95% confidence interval [CI]: 5.2– 17.1, P< 0.001), invasive procedures (OR: 11.1, 95% CI: 3.3– 37.7, P< 0.001), and pre-existing diseases of the digestive system (OR: 8.22, 95% CI: 1.73– 39.2, P=0.008). Treatment failure was more frequent in the cases (84.7%) than in the controls (32.6%).Conclusion: Exposure to antibiotics, especially carbapenems, and invasive procedures were the major risk factors for carbapenem resistance among patients with K. pneumoniae BSIs. Strict control measures should be implemented to prevent the emergence and spread of CRKP.Keywords: antimicrobial resistance, bacteremia, digestive system diseases, treatment failure

Additional file 3. Verification of microbial identification on the Autof MS1000 and Bruker Biotyper

Additional file 1 Adjusted odds ratios and 95% confidence intervals of the association of metabolic health and obesity with high baPWV by sex in 2017 (n = 2076).

Additional file 1. Table S1. Univariate and multivariate Cox analyses for S1P in two subgroups. Table S2. Net reclassification of death and not death with adding S1P to Risk Factors. Figure S1. Association between S1P levels and the hazard ratio for all-cause death.

Additional file 2. MS analysis of common bacteria and yeasts on the Autof MS1000 and Bruker Biotyper

Additional file 1. Identification results on the Autof MS1000 and Bruker Biotyper

Additional file 2 Characteristics of the study participants at baseline and during follow-ups (n = 202).

Phonon polaritons in van der Waals materials reveal significant confinement accompanied with long propagation length: important virtues for tasks pertaining to the control of light and energy flow at the nanoscale. While previous studies of phonon polaritons have relied on relatively thick samples, here reported is the first observation of surface phonon polaritons in single atomic layers and bilayers of hexagonal boron nitride (hBN). Using antenna-based near-field microscopy, propagating surface phonon polaritons in mono- and bilayer hBN microcrystals are imaged. Phonon polaritons in monolayer hBN are confined in a volume about one million times smaller than the free-space photons. Both the polariton dispersion and their wavelength-thickness scaling law are altered compared to those of hBN bulk counterparts. These changes are attributed to phonon hardening in monolayer-thick crystals. The data reported here have bearing on applications of polaritons in metasurfaces and ultrathin optical elements.

Advanced microscopy and/or spectroscopy tools play indispensable role in nanoscience and nanotechnology research, as it provides rich information about the growth mechanism, chemical compositions, crystallography, and other important physical and chemical properties. However, the interpretation of imaging data heavily relies on the "intuition" of experienced researchers. As a result, many of the deep graphical features obtained through these tools are often unused because of difficulties in processing the data and finding the correlations. Such challenges can be well addressed by deep learning. In this work, we use the optical characterization of two-dimensional (2D) materials as a case study, and demonstrate a neural-network-based algorithm for the material and thickness identification of exfoliated 2D materials with high prediction accuracy and real-time processing capability. Further analysis shows that the trained network can extract deep graphical features such as contrast, color, edges, shapes, segment sizes and their distributions, based on which we develop an ensemble approach topredict the most relevant physical properties of 2D materials. Finally, a transfer learning technique is applied to adapt the pretrained network to other applications such as identifying layer numbers of a new 2D material, or materials produced by a different synthetic approach. Our artificial-intelligence-based material characterization approach is a powerful tool that would speed up the preparation, initial characterization of 2D materials and other nanomaterials and potentially accelerate new material discoveries.

A novel ruthenium-catalyzed [5 + 1] annulation of 2-alkenylanilines with sulfoxonium ylides was developed for the rapid assembly of highly functionalized quinolines. This new catalytic process empl...

Unlike conventional plasmonic media, polaritonic van der Waals (vdW) materials hold promise for active control of light-matter interactions. The dispersion relations of elementary excitations such as phonons and plasmons can be tuned in layered vdW systems via stacking using functional substrates. In this work, infrared nanoimaging and nanospectroscopy of hyperbolic phonon polaritons are demonstrated in a novel vdW heterostructure combining hexagonal boron nitride (hBN) and vanadium dioxide (VO₂). It is observed that the insulator-to-metal transition in VO₂ has a profound impact on the polaritons in the proximal hBN layer. In effect, the real-space propagation of hyperbolic polaritons and their spectroscopic resonances can be actively controlled by temperature. This tunability originates from the effective change in local dielectric properties of the VO₂ sublayer in the course of the temperature-tuned insulator-to-metal phase transition. The high susceptibility of polaritons to electronic phase transitions opens new possibilities for applications of vdW materials in combination with strongly correlated quantum materials. Keywords: hexagonal boron nitride; phase-change materials; polaritons

Recent theoretical advances have proposed a new class of topological crystalline insulator (TCI) phases protected by rotational symmetries. Distinct from topological insulators (TIs), rotational symmetry-protected TCIs are expected to show unique topologically protected boundary modes: First, the surface normal to the rotational axis features unpinned Dirac surface states whose Dirac points are located at generic k points. Second, due to the higher-order bulk boundary correspondence, a 3D TCI also supports 1D helical edge states. Despite the unique topological electronic properties, to date, purely rotational symmetry-protected TCIs remain elusive in real materials. Using first-principles band calculations and theoretical modeling, we identify the van der Waals material $��$-Bi4Br4 as a TCI purely protected by rotation symmetry. We show that the Bi4Br4's (010) surface exhibits a pair of unpinned topological Dirac fermions protected by the two-fold rotational axis. These unpinned Dirac fermions show an exotic spin texture highly favorable for spin transport and a band structure consisting of van Hove singularities due to Lifshitz transition. We also identify 1D topological hinge states along the edges of an $��$-Bi4Br4 rod. We further discuss how the proposed topological electronic properties in $��$-Bi4Br4 can be observed by various experimental techniques.

The observation of chirality is ubiquitous in nature. Contrary to intuition, the population of opposite chiralities is surprisingly asymmetric at fundamental levels. Examples range from parity violation in the subatomic weak force to the homochirality in essential biomolecules. The ability to achieve chirality-selective synthesis (chiral induction) is of great importance in stereochemistry, molecular biology and pharmacology. In condensed matter physics, a crystalline electronic system is geometrically chiral when it lacks any mirror plane, space inversion center or roto-inversion axis. Typically, the geometrical chirality is predefined by a material's chiral lattice structure, which is fixed upon the formation of the crystal. By contrast, a particularly unconventional scenario is the gyrotropic order, where chirality spontaneously emerges across a phase transition as the electron system breaks the relevant symmetries of an originally achiral lattice. Such a gyrotropic order, proposed as the quantum analogue of the cholesteric liquid crystals, has attracted significant interest. However, to date, a clear observation and manipulation of the gyrotropic order remain challenging. We report the realization of optical chiral induction and the observation of a gyrotropically ordered phase in the transition-metal dichalcogenide semimetal $1T$-TiSe$_2$. We show that shining mid-infrared circularly polarized light near the critical temperature leads to the preferential formation of one chiral domain. As a result, we are able to observe an out-of-plane circular photogalvanic current, whose direction depends on the optical induction. Our study provides compelling evidence for the spontaneous emergence of chirality in the correlated semimetal TiSe$_2$. Such chiral induction provides a new way of optical control over novel orders in quantum materials., Comment: 22 pages, 5 figures

We investigated emission and propagation of polaritons in a two dimensional van der Waals material hexagonal boron nitride (hBN). Our specific emphasis in this work is on hyperbolic phonon polariton emission that we investigated by means of scattering-type scanning near-field optical microscopy. Real-space nano-images detail how the polaritons are launched in several common arrangements including: light scattering by the edges of the crystal, metallic nanostructures deposited on the surface of hBN crystals, as well as random defects and impurities. Notably, the scanned tip of the near-field microscope is itself an efficient polariton launcher. Our analysis reveals that the scanning tips are superior to other types of emitters we have investigated. Furthermore, the study of polariton emission and emission efficiency may provide insights for development of polaritonic devices and for fundamental studies of collective modes in other van der Waals materials., 19 pages, 3 figures

Diverse parallel stitched two-dimensional heterostructures are synthesized, including metal-semiconductor (graphene-MoS2), semiconductor-semiconductor (WS2-MoS2), and insulator-semiconductor (hBN-MoS2), directly through selective sowing of aromatic molecules as the seeds in chemical vapor deposition (CVD) method. Our methodology enables the large-scale fabrication of lateral heterostructures with arbitrary patterns, and clean and precisely aligned interfaces, which offers tremendous potential for its application in integrated circuits., 30 pages, 4 figures, Accepted by Advanced Materials

Complex odontoma is a relatively rare dental dysplasia. In particular, a complex odontoma with dentigerous cyst is seldom observed. A case of complex odontoma with dentigerous cyst is reported in this paper.

Based on the introduction of the natural and geographic conditions in Bayingolin Mongol Autonomous Prefecture in Xinjiang(Bazhou), development status of Korla Fragrant Pear is introduced from the two aspects of the production status and the storage and processing status of Korla Fragrant Pear. Among them, production status of Korla Fragrant Pear is analyzed from the aspects of the rapid growth of planting area and the stable growth of output. And the storage and processing status of Korla Fragrant Pear is introduced from the aspects of the development status of the storage industry and the development status of processing industry, and the status of domestic and foreign marketing. Problems in the industrialization development of Korla Fragrant Pear in Bazhou are analyzed, such as the weak protection of brand and lack of external propaganda, the imperfect benefit affiliating mechanism between leading enterprises and peasant households, and the marketing network of Korla Fragrant Pear and single mode of marketing. Countermeasures for the acceleration of the industrial development of Korla Fragrant Pear in Bazhou are put forward, such as making great efforts at publicity, brand establishment and counterfeit prevention, cultivating leading enterprises, reducing market risk, implementing industrialization development, adopting various marketing forms and actively developing domestic and international markets.

Based on the introduction of the natural and geographic conditions in Bayingolin Mongol Autonomous Prefecture in Xinjiang(Bazhou), development status of Korla Fragrant Pear is introduced from the two aspects of the production status and the storage and processing status of Korla Fragrant Pear. Among them, production status of Korla Fragrant Pear is analyzed from the aspects of the rapid growth of planting area and the stable growth of output. And the storage and processing status of Korla Fragrant Pear is introduced from the aspects of the development status of the storage industry and the development status of processing industry, and the status of domestic and foreign marketing. Problems in the industrialization development of Korla Fragrant Pear in Bazhou are analyzed, such as the weak protection of brand and lack of external propaganda, the imperfect benefit affiliating mechanism between leading enterprises and peasant households, and the marketing network of Korla Fragrant Pear and single mode of marketing. Countermeasures for the acceleration of the industrial development of Korla Fragrant Pear in Bazhou are put forward, such as making great efforts at publicity, brand establishment and counterfeit prevention, cultivating leading enterprises, reducing market risk, implementing industrialization development, adopting various marketing forms and actively developing domestic and international markets.

We propose a new method to use gapped graphene as barrier to confine electrons in gapless graphene and form a good quantum dot, which can be realized on an oxygen-terminated $SiO_{2}$ substrate partly H-passivated. In particular, we use ferromagnetic insulators deposited on top of barrier which give rise to a spin related energy spectrum and transport properties. Compared to the complexity of etched quantum dots in graphene, the setup suggested here is a promising candidate for practical applications.

Taking the Jiuquan City, Guansu Provice, China as an example, according to the 1997-2007 Gansu Statistical Yearbook, Jiuquan Statistical Yearbook, the Second National Land Investigation in Jiuquan City and other relevant statistical data, models of minimum cultivated area per capita and pressure index of cultivated land are used based on food security. Cultivated land area, population, grain output, sowing area and other factors in years 1997-2007, which affect the cultivated land pressure in arid and semi-arid areas, are analyzed and estimated, as well as the temporal variations of minimum cultivated area per capita and pressure index of cultivated land. Pressure index of cultivated land in Jiuquan City is calculated and the pressure situation of cultivated land at present is analyzed. Based on the construction of demand function of cultivated land, demand of cultivated land, that is, the protected area of basic farmland and cultivated land, is finally obtained so as to achieve the goal of food security in Jiuquan City at the stage of comprehensive construction of a well-off society in the year 2020. Considering the food security of China, we use PSR Model and find out that it is necessary to strengthen government’s macro-control functions, to protect the fragile ecological environment, to improve the land intensive and economical use during the process of urbanization, and to reduce the pressure of cultivated land in arid and semi-arid region, and to provide theoretical basis for the policy making of cultivated land protection in this region.

We study the conductance spectrum of graphene quantum dots, both single and multiple cases. The single electron tunneling phenomenon is investigated and the periodicity, amplitude and line shape of the Coulomb blockade oscillations at low temperatures are obtained. Further, we discuss the transport behavior when multiple dots are assembled in array and find a phase transition of conductance spectra from individual Coulomb blockade to collective Coulomb blockade., Comment: 7 pages, 6 figures

Taking the Jiuquan City, Guansu Provice, China as an example, according to the 1997-2007 Gansu Statistical Yearbook, Jiuquan Statistical Yearbook, the Second National Land Investigation in Jiuquan City and other relevant statistical data, models of minimum cultivated area per capita and pressure index of cultivated land are used based on food security. Cultivated land area, population, grain output, sowing area and other factors in years 1997-2007, which affect the cultivated land pressure in arid and semi-arid areas, are analyzed and estimated, as well as the temporal variations of minimum cultivated area per capita and pressure index of cultivated land. Pressure index of cultivated land in Jiuquan City is calculated and the pressure situation of cultivated land at present is analyzed. Based on the construction of demand function of cultivated land, demand of cultivated land, that is, the protected area of basic farmland and cultivated land, is finally obtained so as to achieve the goal of food security in Jiuquan City at the stage of comprehensive construction of a well-off society in the year 2020. Considering the food security of China, we use PSR Model and find out that it is necessary to strengthen government’s macro-control functions, to protect the fragile ecological environment, to improve the land intensive and economical use during the process of urbanization, and to reduce the pressure of cultivated land in arid and semi-arid region, and to provide theoretical basis for the policy making of cultivated land protection in this region.

Diverse parallel stitched 2D heterostructures, including metal–semiconductor, semiconductor–semiconductor, and insulator–semiconductor, are synthesized directly through selective “sowing” of aromatic molecules as the seeds in the chemical vapor deposition (CVD) method. The methodology enables the large-scale fabrication of lateral heterostructures, which offers tremendous potential for its application in integrated circuits., Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Award No. 023674), National Science Foundation (U.S.). Division of Materials Research. (Award No. 1004147), United States. Department of Energy. (Award No. DE-SC0001299), United States. Office of Naval Research. Presidential Early Career Award for Scientists and Engineers (Award No. 021302-001), United States. Department of Energy. (Contract No. DE-AC02-98CH10886), China. Ministry of Science and Technology. (MOST 103-2112-M-007-001-MY3)

Ultrafast electron thermalization—the process leading to carrier multiplication via impact ionization and hot-carrier luminescence —occurs when optically excited electrons in a material undergo rapid electron–electron scattering to redistribute excess energy and reach electronic thermal equilibrium. Owing to extremely short time and length scales, the measurement and manipulation of electron thermalization in nanoscale devices remains challenging even with the most advanced ultrafast laser techniques. Here, we overcome this challenge by leveraging the atomic thinness of two-dimensional van der Waals (vdW) materials to introduce a highly tunable electron transfer pathway that directly competes with electron thermalization. We realize this scheme in a graphene–boron nitride–graphene (G–BN–G) vdW heterostructure through which optically excited carriers are transported from one graphene layer to the other. By applying an interlayer bias voltage or varying the excitation photon energy, interlayer carrier transport can be controlled to occur faster or slower than the intralayer scattering events, thus effectively tuning the electron thermalization pathways in graphene. Our findings, which demonstrate a means to probe and directly modulate electron energy transport in nanoscale materials, represent a step towards designing and implementing optoelectronic and energy-harvesting devices with tailored microscopic properties., United States. Air Force Office of Scientific Research (FA9550-11-1-0225), National Science Foundation (U.S.) (DMR-1231319)

Hexagonal boron nitride (h-BN) is a natural hyperbolic material, for which the dielectric constants are the same in the basal plane (epsilon^t = epsilon^x = epsilon^y) but have opposite signs (epsilon^t*epsilon^z < 0) from that in the normal plane (epsilon^z). Due to this property, finite-thickness slabs of h-BN act as multimode waveguides for propagation of hyperbolic phonon polaritons - collective modes that originate from the coupling between photons and electric dipoles in phonons. However, control of these hyperbolic phonon polaritons modes has remained challenging, mostly because their electrodynamic properties are dictated by the crystal lattice of h-BN. Here we show by direct nano-infrared imaging that these hyperbolic polaritons can be effectively modulated in a van der Waals heterostructure composed of monolayer graphene on h-BN. Tunability originates from the hybridization of surface plasmon polaritons in graphene with hyperbolic phonon polaritons in h-BN, so that the eigenmodes of the graphene/h-BN heterostructure are hyperbolic plasmon-phonon polaritons. Remarkably, the hyperbolic plasmon-phonon polaritons in graphene/h-BN suffer little from ohmic losses, making their propagation length 1.5-2.0 times greater than that of hyperbolic phonon polaritons in h-BN. The hyperbolic plasmon-phonon polaritons possess the combined virtues of surface plasmon polaritons in graphene and hyperbolic phonon polaritons in h-BN. Therefore, graphene/h-BN structures can be classified as electromagnetic metamaterials since the resulting properties of these devices are not present in its constituent elements alone., 20 pages, 3 figures in Nature Nanotechnology 2015

et al., Optoelectronic devices utilizing graphene have demonstrated unique capabilities and performances beyond state-of-the-art technologies. However, requirements in terms of device quality and uniformity are demanding. A major roadblock towards high-performance devices are nanoscale variations of the graphene device properties, impacting their macroscopic behaviour. Here we present and apply non-invasive optoelectronic nanoscopy to measure the optical and electronic properties of graphene devices locally. This is achieved by combining scanning near-field infrared nanoscopy with electrical read-out, allowing infrared photocurrent mapping at length scales of tens of nanometres. Using this technique, we study the impact of edges and grain boundaries on the spatial carrier density profiles and local thermoelectric properties. Moreover, we show that the technique can readily be applied to encapsulated graphene devices. We observe charge build-up near the edges and demonstrate a solution to this issue., F.H.L.K. acknowledges financial support from the Spanish Ministry of Economy and Competitiveness, through the ‘Severo Ochoa’ Programme for Centres of Excellence in R&D (SEV-2015-0522), support by Fundacio Cellex Barcelona, the ERC Career integration grant (294056, GRANOP), the ERC starting grant (307806, CarbonLight), the Government of Catalonia trough the SGR grant (2014-SGR-1535), the Mineco grants Ramón y Cajal (RYC-2012-12281) and Plan Nacional (FIS2013-47161-P), and project GRASP (FP7-ICT-2013-613024-GRASP). F.H.L.K. and R.H. acknowledge support by the E.C. (European Commission) under Graphene Flagship (contract no. CNECT-ICT604391). D.J. acknowledges support from the Ramón y Cajal Fellowship Program. Y.G. and J.H. acknowledge support from the US Office of Naval Research N00014-13-1-0662. We acknowledge financial support from the Spanish Ministry of Economy and Competitiveness and ‘Fondo Europeo de Desarrollo Regional’ through Grant TEC2013-46168-R. Q.M. and P.J.-H. have been supported by AFOSR Grant No. FA9550-11-1-0225 and the Packard Fellowship program. This work made use of the Materials Research Science and Engineering Center Shared Experimental Facilities supported by the National Science Foundation (NSF) (Grant No. DMR-0819762) and of Harvard’s Center for Nanoscale Systems, supported by the NSF (Grant No. ECS-0335765). S.R. acknowledges the Spanish Ministry of Economy and Competitiveness for funding (MAT2012-33911), the Secretaria de Universidades e Investigacion del Departamento de Economia y Conocimiento de la Generalidad de Catalunya and the Severo Ochoa Program (MINECO SEV-2013-0295). J.E.B.-V. acknowledges support from SECITI (Mexico, D.F.).

Uniaxial materials whose axial and tangential permittivities have opposite signs are referred to as indefinite or hyperbolic media. In such materials, light propagation is unusual leading to novel and often non-intuitive optical phenomena. Here we report infrared nano-imaging experiments demonstrating that crystals of hexagonal boron nitride, a natural mid-infrared hyperbolic material, can act as a ‘hyper-focusing lens’ and as a multi-mode waveguide. The lensing is manifested by subdiffractional focusing of phonon–polaritons launched by metallic disks underneath the hexagonal boron nitride crystal. The waveguiding is revealed through the modal analysis of the periodic patterns observed around such launchers and near the sample edges. Our work opens new opportunities for anisotropic layered insulators in infrared nanophotonics complementing and potentially surpassing concurrent artificial hyperbolic materials with lower losses and higher optical localization., United States. Air Force Office of Scientific Research (Grant FA9550-11-1-0225)

Photoexcitation of graphene leads to an interesting sequence of phenomena, some of which can be exploited in optoelectronic devices based on graphene. In particular, the efficient and ultrafast generation of an electron distribution with an elevated electron temperature and the concomitant generation of a photo-thermoelectric voltage at symmetry-breaking interfaces is of interest for photosensing and light harvesting. Here, we experimentally study the generated photocurrent at the graphene–metal interface, focusing on the time-resolved photocurrent, the effects of photon energy, Fermi energy and light polarization. We show that a single framework based on photo-thermoelectric photocurrent generation explains all experimental results., United States. Air Force Office of Scientific Research (Grant FA9550-11-1-0225), David & Lucile Packard Foundation (Fellowship)

van der Waals heterostructures assembled from atomically thin crystalline layers of diverse two-dimensional solids are emerging as a new paradigm in the physics of materials. We used infrared nanoimaging to study the properties of surface phonon polaritons in a representative van der Waals crystal, hexagonal boron nitride. We launched, detected, and imaged the polaritonic waves in real space and altered their wavelength by varying the number of crystal layers in our specimens. The measured dispersion of polaritonic waves was shown to be governed by the crystal thickness according to a scaling law that persists down to a few atomic layers. Our results are likely to hold true in other polar van der Waals crystals and may lead to new functionalities., United States. Air Force Office of Scientific Research (Grant FA9550-11-1-0225)