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Van der Waals interactions with transition metal dichalcogenides were shown to induce strong spin-orbit coupling (SOC) in graphene, offering great promises to combine large experimental flexibility of graphene with unique tuning capabilities of the SOC. Here, we probe SOC-driven band splitting and electron dynamics in graphene on WSe2 by measuring ballistic transverse magnetic focusing. We found a clear splitting in the first focusing peak whose evolution in charge density and magnetic field is well reproduced by calculations using the SOC strength of ~ 13 meV, and no splitting in the second peak that indicates stronger Rashba SOC. Possible suppression of electron-electron scatterings was found in temperature dependence measurement. Further, we found that Shubnikov-de Haas oscillations exhibit a weaker band splitting, suggesting that it probes different electron dynamics, calling for a new theory. Our study demonstrates an interesting possibility to exploit ballistic electron motion pronounced in graphene for emerging spin-orbitronics. By combining graphene with transition metal dichalcogenides, such as WSe2, it is possible to induce a large spin-orbit interaction in the graphene layer. Here, Rao et al study the spin-orbit coupling in graphene/WSe2 heterostructures using the ballistic transport based technique, known transverse magnetic focusing. [ABSTRACT FROM AUTHOR]

The presence of periodic modulation in graphene leads to a reconstruction of the band structure and formation of minibands. In an external uniform magnetic field, a fractal energy spectrum called Hofstadter butterfly is formed. Particularly interesting in this regard are superlattices with tunable modulation strength, such as electrostatically induced ones in graphene. We perform quantum transport modeling in gate-induced square two-dimensional superlattice in graphene and investigate the relation to the details of the band structure. At low magnetic field the dynamics of carriers reflects the semi-classical orbits which depend on the mini band structure. We theoretically model transverse magnetic focusing, a ballistic transport technique by means of which we investigate the minibands, their extent and carrier type. We find a good agreement between the focusing spectra and the mini band structures obtained from the continuum model, proving usefulness of this technique. At high magnetic field the calculated four-probe resistance fit the Hofstadter butterfly spectrum obtained for our superlattice. Our quantum transport modeling provides an insight into the mini band structures, and can be applied to other superlattice geometries. [ABSTRACT FROM AUTHOR]

Chinese medicine (CM) has thousands of years of experience in prevention of diseases. As for CM, people's constitution is closely related to their health status, thus recognition of CM constitution is the fundamental and core content of research on constitution types. With development of technologies such as sensors, artificial intelligence and big data, objectification of the four diagnostic methods of CM has gradually matured, bringing changes in the mindset and innovations in technical means for recognition of CM constitution. This paper presents a systematic review of the latest research trends in constitution recognition based on objectification of diagnostic methods in CM. [ABSTRACT FROM AUTHOR]

The constituent particles of matter can arrange themselves in various ways, giving rise to emergent phenomena that can be surprisingly rich and often cannot be understood by studying only the individual constituents. Discovering and understanding the emergence of such phenomena in quantum materials—especially those in which multiple degrees of freedom or energy scales are delicately balanced—is of fundamental interest to condensed-matter research1,2. Here we report on the surprising observation of emergent ferroelectricity in graphene-based moiré heterostructures. Ferroelectric materials show electrically switchable electric dipoles, which are usually formed by spatial separation between the average centres of positive and negative charge within the unit cell. On this basis, it is difficult to imagine graphene—a material composed of only carbon atoms—exhibiting ferroelectricity3. However, in this work we realize switchable ferroelectricity in Bernal-stacked bilayer graphene sandwiched between two hexagonal boron nitride layers. By introducing a moiré superlattice potential (via aligning bilayer graphene with the top and/or bottom boron nitride crystals), we observe prominent and robust hysteretic behaviour of the graphene resistance with an externally applied out-of-plane displacement field. Our systematic transport measurements reveal a rich and striking response as a function of displacement field and electron filling, and beyond the framework of conventional ferroelectrics. We further directly probe the ferroelectric polarization through a non-local monolayer graphene sensor. Our results suggest an unconventional, odd-parity electronic ordering in the bilayer graphene/boron nitride moiré system. This emergent moiré ferroelectricity may enable ultrafast, programmable and atomically thin carbon-based memory devices. Electronic ferroelectricity is observed in a graphene-based moiré heterostructure, which is explained using a spontaneous interlayer charge-transfer model driven by layer-specific on-site Coulomb repulsion. [ABSTRACT FROM AUTHOR]

Electrostatic superlattices have been known to significantly modify the electronic structure of low-dimensional materials. Studies of graphene superlattices were triggered by the discovery of moiré patterns in van der Waals stacks of graphene and hexagonal boron nitride (hBN) layers a few years ago. Very recently, gate-controllable superlattices using spatially modulated gate oxides have been achieved, allowing for Dirac band structure engineering of graphene. Despite these rapid experimental progresses, technical advances in quantum transport simulations for large-scale graphene superlattices have been relatively limited. Here, we show that transport experiments for both graphene/hBN moiré superlattices and gate-controllable superlattices can be well reproduced by transport simulations based on a scalable tight-binding model. Our finding paves the way to tuning-parameter-free quantum transport simulations for graphene superlattices, providing reliable guides for understanding and predicting novel electric properties of complex graphene superlattice devices. The electronic structure of graphene can be modified by applying the so-called superlattice potential, arising either from interfacing with hexagonal boron nitride lattices or gate capacitance with spatially periodic modulation, giving rise to a range of unusual transport behavior. Here, the authors report a simulation method to reproduce transport experiments, showing consistent transmission spectra and mini-band structures for graphene superlattices. [ABSTRACT FROM AUTHOR]

The distribution and variations of permafrost in the Xidatan region, the northern permafrost boundary of the Qinghai-Tibet Plateau, were examined and analyzed using ground penetrating radar (GPR), borehole drilling, and thermal monitoring data. Results from GPR profiles together with borehole verification indicate that the lowest elevation limit of permafrost occurrence is 4369 m above sea level in 2012. Compared to previous studies, the maximal rise of permafrost limit is 28 m from 1975 to 2012. The total area of permafrost in the study region has been decreased by 13.8%. One of the two previously existed permafrost islands has disappeared and second one has reduced by 76% in area during the past ~40 years. In addition, the ground temperature in the Xidatan region has increased from 2012 to 2016, with a mean warming rate of ~0.004°C a−1 and ~0.003°C a−1 at the depths of 6 and 15 m, respectively. The rising of permafrost limit in the Xidatan region is mainly due to global warming. However, some non-climatic factors such as hydrologic processes and anthropic disturbances have also induced permafrost degradation. If the air temperature continues to increase, the northern permafrost boundary in the Qinghai-Tibet Plateau may continue rising in the future. [ABSTRACT FROM AUTHOR]

It has been proven that crushed rock layers used in roadbed construction in permafrost regions have a cooling effect. The main reason is the existence of large porosity of the rock layers. However, due to the strong winds, cold and high radiation conditions on the Qinghai−Tibet Plateau (QTP), both wind-blown sand and/or weathered rock debris blockage might reduce the porosity of the rock layers, resulting in weakening the cooling effect of the crushed rock layer (CRL) in the crushed rock embankment (CRE) of the Qinghai−Tibet Railway (QTR) in the permafrost regions. Such a process might warm the underlying permafrost, and further lead to potential threat to the QTR's integrity and stability. The different porosities corresponding to the different equivalent rock diameters were measured in the laboratory using water saturation method, and an empirical exponential equation between porosity and equivalent rock diameter was proposed based on the measured experimental data and an important finding is observed in our and other experiments that the larger size crushed rock tends to lead to the larger porosity when arbitrarily packing. Numerical tests were carried out to study impacts of porosity on permafrost degradation and differential thaw depths between the sunny and shady shoulders. The results show that the decrease in porosity due to wind-blown sand or weathered rock debris clogging can worsen the permafrost degradation and lead to the asymmetric thermal regime. In the traditional embankment (without the CRL within it), the largest differential thaw depth can reach up to 3.1 m. The optimized porosity appears in a range from 34% to 42% corresponding to equivalent rock diameter from 10 to 20.5 cm. The CRE with the optimized porosities can make underlying permafrost stable and 0 °C isotherms symmetric in the coming 50 years, even under the condition that the climate warming can lead to permafrost degradation under the CRE and the traditional embankment. Some practical implications were proposed to benefit the future design, construction and maintenance of CRE in permafrost regions. [ABSTRACT FROM AUTHOR]

Knowledge of the spatial distribution of permafrost and the effects of climate on ground temperature are important for land use and infrastructure development on the Qinghai-Tibet Plateau (QTP). Different permafrost models have been developed to simulate the ground temperature and active layer thickness (ALT). In this study, Temperature at Top of Permafrost (TTOP) model, Kudryavtsev model and modified Stefan solution were evaluated against detailed field measurements at four distinct field sites in the Wudaoliang Basin to better understand the applicability of permafrost models. Field data from 2012 to 2014 showed that there were notable differences in observed ground temperatures and ALTs within and among the sites. The TTOP model is relatively simple, however, when driven by averaged input values, it produced more accurate permafrost surface temperature (Tps) than the Kudryavtsev model. The modified Stefan solution resulted in a satisfactory accuracy of 90%, which was better than the Kudryavtsev model for estimating ALTs. The modified Stefan solution had the potential of being applied to climate-change studies in the future. Furthermore, additional field investigations over longer periods focusing on hydrology, which has significant influence on permafrost thaw, are necessary. These efforts should employ advanced measurement techniques to obtain adequate and extensive local parameters that will help improve model accuracy. [ABSTRACT FROM AUTHOR]