The study of spatial symmetries was accomplished during the last century and had greatly improved our understanding of the properties of solids. Nowadays, the symmetry data of any crystal can be ...readily extracted from standard first-principles calculation. On the other hand, the topological data (topological invariants), the defining quantities of nontrivial topological states, are in general considerably difficult to obtain, and this difficulty has critically slowed down the search for topological materials. Here we provide explicit and exhaustive mappings from symmetry data to topological data for arbitrary gapped band structure in the presence of time-reversal symmetry and any one of the 230 space groups. The mappings are completed using the theoretical tools of layer construction and symmetry-based indicators. With these results, finding topological invariants in any given gapped band structure reduces to a simple search in the mapping tables provided.
Quantum spin Hall (QSH) insulators, a new class of quantum matter, can support topologically protected helical edge modes inside a bulk insulating gap, which can lead to dissipationless transport. A ...major obstacle to reaching a wide application of QSH is the lack of suitable QSH compounds, which should be easily fabricated and have a large bulk gap. Here, we predict that single-layer ZrTe5 and HfTe5 are the most promising candidates for large-gap insulators, with a bulk direct (indirect) band gap as large as 0.4 eV (0.1 eV) and which are robust against external strains. The three-dimensional crystals of these two materials are good layered compounds with very weak interlayer bonding, and they are located near the phase boundary between weak and strong topological insulators, paving a new way for future experimental studies on both the QSH effect and topological phase transitions.
Based on first-principles calculations and effective model analysis, we propose that the WC-type HfC, in the absence of spin-orbit coupling (SOC), can host a three-dimensional nodal chain semimetal ...state. Distinguished from the previous material IrF_{4} T. Bzdusek et al., Nature 538, 75 (2016), the nodal chain here is protected by mirror reflection symmetries of a simple space group, while in IrF_{4} the nonsymmorphic space group with a glide plane is a necessity. Moreover, in the presence of SOC, the nodal chain in WC-type HfC evolves into Weyl points. In the Brillouin zone, a total of 30 pairs of Weyl points in three types are obtained through the first-principles calculations. Besides, the surface states and the pattern of the surface Fermi arcs connecting these Weyl points are studied, which may be measured by future experiments.
Next-generation polarized mid-infrared imaging systems generally requires miniaturization, integration, flexibility, good workability at room temperature and in severe environments, etc. Emerging ...two-dimensional materials provide another route to meet these demands, due to the ease of integrating on complex structures, their native in-plane anisotropy crystal structure for high polarization photosensitivity, and strong quantum confinement for excellent photodetecting performances at room temperature. However, polarized infrared imaging under scattering based on 2D materials has yet to be realized. Here we report the systematic investigation of polarized infrared imaging for a designed target obscured by scattering media using an anisotropic tellurium photodetector. Broadband sensitive photoresponse is realized at room temperature, with excellent stability without degradation under ambient atmospheric conditions. Significantly, a large anisotropic ratio of tellurium ensures polarized imaging in a scattering environment, with the degree of linear polarization over 0.8, opening up possibilities for developing next-generation polarized mid-infrared imaging technology.
It is of great significance to study the impact of financial development on carbon emissions for the development of low-carbon economy. Although many empirical studies reveal significant correlations ...between financial development and various environmental pollution variables, few studies differentiate financial scale and efficiency from other factors, and pay attention to the impact of securities capital market on carbon emissions. In view of the complexity of financial development impact mechanism on carbon emissions in China, this paper classifies financial development into two dimensions: financial scale and securities size. We establish a broader autoregressive distributed lag-error correction model (ARDL-ECM), which is used to measure the dynamic relationship among financial scale, securities size, urbanization, economic development, trade openness and China’s carbon emission intensity. The study indicates that there is positive short-run and long-run relationship among financial scale, economic growth and carbon emission intensity. This reflects that the current development of financial scale has stimulated the development of China’s economy, but brought carbon emissions. The size of securities has a relatively small impact on carbon emission intensity both in the short run and long run. This shows that China’s current securities market mechanism of regulating carbon emissions needs further improvement. The above conclusions are convinced by the robustness tests. This paper provides empirical evidence for policy makers to support the implementation of financial and low carbon economy growth.
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•The extend autoregressive distributed lag-error correction model is adopted.•Financial development is closely related to economic and ecological environment.•The impact of securities size is relatively small.•The positive effect exists both in the short run and long run.
Graphite anode suffers from great capacity loss and even fails to charge (i.e. Li+‐intercalation) under low temperature, mainly arising from the large overpotential including sluggish de‐solvation ...process and insufficient ions movement in the solid electrolyte interphase (SEI). Herein, an electrolyte is developed by utilizing weakly solvated molecule ethyl trifluoroacetate and film‐forming fluoroethylene carbonate to achieve smooth de‐solvation and high ionic conductivity at low temperature. Evolution of SEI formed at different temperatures is further investigated to propose an effective room‐temperature SEI formation strategy for low‐temperature operations. The synergetic effect of tamed electrolyte and optimized SEI enables graphite with a reversible charge/discharge capacity of 183 mAh g−1 at −30 °C and fast‐charging up to 6C‐rate at room temperature. Moreover, graphite||LiFePO4 full cell maintains a capacity retention of 78 % at −30 °C, and 37 % even at a super‐low temperature of −60 °C. This work offers a progressive insight towards fast‐charging and low‐temperature batteries.
This work offers a weakly‐solvated electrolyte and a high‐quality SEI by room‐temperature formation process, which enables graphite electrode with a fast‐charging 6C‐rate and low‐temperature operation. Moreover, the Gr||LiFePO4 full cell exhibits a capacity retention of 78 % at −30 °C and a high discharge capacity of 37 % even at −60 °C.
Based on first-principle calculations, we show that a family of nonmagnetic materials including TaAs, TaP, NbAs, and NbP are Weyl semimetals (WSM) without inversion centers. We find twelve pairs of ...Weyl points in the whole Brillouin zone (BZ) for each of them. In the absence of spin-orbit coupling (SOC), band inversions in mirror-invariant planes lead to gapless nodal rings in the energy-momentum dispersion. The strong SOC in these materials then opens full gaps in the mirror planes, generating nonzero mirror Chern numbers and Weyl points off the mirror planes. The resulting surface-state Fermi arc structures on both (001) and (100) surfaces are also obtained, and they show interesting shapes, pointing to fascinating playgrounds for future experimental studies.
Direct measuring of CO2 flux remains challenging for global lakes. The traditional sampling and gas transfer models used to estimate lake CO2 fluxes are variable and uncertain, and ice‐covered ...periods are often excluded from the annual carbon budget. Here, the first longtime (2013−2017) direct measurement of CO2 flux by eddy covariance system over the largest saline lake (Qinghai lake) in the Qinghai‐Tibet Plateau (QTP) revealed that ice‐covered period draws large amounts of CO2 from the atmosphere (−0.87 ± 0.38 g C m−2 d−1), a value more than twice the CO2 flux rate during the ice‐free period (−0.41 ± 0.35 g C m−2 d−1). The total CO2 uptake by all saline lakes on the QTP was estimated to −10.28 ± 1.65 Tg C yr−1, an equivalent to approximately one third of the net terrestrial ecosystems carbon sink in QTP. Our results indicate large sink for CO2 in winter is controlled by both seasonal hydrochemistry processes and lake ice absorption in saline lakes. This research also demonstrates decreasing CO2 uptake from the atmosphere by saline lakes on the QTP, which may turn carbon sinks to carbon sources with future warming.
The first direct measurement of CO2 flux over Qinghai lake revealed that significant winter CO2 uptake by saline lakes controlled by seasonal hydrochemistry processes and lake ice absorption on the Qinghai‐Tibet Plateau (QTP). The finding highlights the importance of ice‐covered period for saline lakes in global carbon budge. All saline lakes on the QTP draw 10.28 ± 1.65 Tg C yr−1 CO2 from the atmosphere, an equivalent to approximately one‐third of the net terrestrial ecosystems carbon sink in the QTP. Increasing future climate warming may change saline lakes from carbon sinks to carbon sources by end‐2000s.
By using first-principles calculations, we propose that WC-type ZrTe is a new type of topological semimetal (TSM). It has six pairs of chiral Weyl nodes in its first Brillouin zone, but it is ...distinguished from other existing TSMs by having an additional two paris of massless fermions with triply degenerate nodal points as proposed in the isostructural compounds TaN and NbN. The mirror symmetry, threefold rotational symmetry, and time-reversal symmetry require all of the Weyl nodes to have the same velocity vectors and locate at the same energy level. The Fermi arcs on different surfaces are shown, which may be measured by future experiments. It demonstrates that the “material universe” can support more intriguing particles simultaneously.
Cisplatin is a first‐line drug in clinical cancer treatment but its efficacy is often hindered by chemoresistance in cancer cells. Reduced intracellular drug accumulation is revealed to be a major ...mechanism of cisplatin resistance. Nanoscale drug delivery systems could help to overcome this problem because of their more active cellular uptake and more accurate tumor localization. DNA nanostructures have emerged as promising drug delivery systems because of their intrinsic biocompatibility and structural programmability. Herein, three diverse DNA nanostructures are constructed and their potential for cisplatin prodrug delivery is investigated. Results found that these DNA nanostructures could remarkably enhance the cellular internalization of platinum drugs and thus increase the anticancer activity, not only to regular lung cancer cells (A549), but more importantly to cisplatin‐resistant cancer cells (A549cisR). Further, in vivo studies also demonstrate that cisplatin prodrug loaded DNA nanostructures could effectively suppress tumor growth in both regular and cisplatin‐resistant tumor models. This study suggests that DNA nanostructures are effective carriers for platinum prodrug delivery to combat chemoresistance.
Three DNA nanostructures with varied sizes and shapes are constructed and their efficiency as Pt(IV) prodrug delivery systems to combat chemoresistance are investigated. This study has revealed that 6x6x64nt‐Pt(IV), which markedly enhances the cellular internalization of platinum drugs and shows high tumor passive targeting ability, is the optimal design for Pt(IV) prodrug delivery in vitro and in vivo.
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