Hydrogen production by catalytic water splitting using sunlight holds great promise for clean and sustainable energy source. Despite the efforts made in the past decades, challenges still exist in pursuing solid catalysts with light-harvesting capacity, large surface areas and efficient utilities of the photogenerated carrier, at the same time. Here, a multiple structure design strategy leading to highly enhanced photocatalytic performance on hydrogen production from water splitting in Dion-Jacobson perovskites KCa2Nan-3NbnO3n+1 is described. Specifically, chemical doping (N/Nb4+) of the parent oxides via ammoniation improved the ability of sunlight harvesting efficiently; subsequent liquid exfoliation of the doped perovskites yielded ultrathin [Ca2Nan-3NbnO3n+1](-) nanosheets with greatly increased surface areas. Significantly, the maximum hydrogen evolution appears in the n=4 nanosheets, which suggests the most favorable thickness for charge separation in such perovskite-type catalysts. The optimized black N/Nb4+-[Ca2NaNb4O13](-) nanosheets show greatly enhanced photocatalytic performance, as high as 973 mu molh(-1) with Pt loading, on hydrogen evolution from water splitting. As a proof-of-concept, this work highlights the feasibility of combining various chemical strategies towards better catalysts and precise thickness control of two-dimensional materials.

Weyl semimetal defines a material with three-dimensional Dirac cones, which appear in pair due to the breaking of spatial inversion or time reversal symmetry. Superconductivity is the state of quantum condensation of paired electrons. Turning a Weyl semimetal into superconducting state is very important in having some unprecedented discoveries. In this work, by doing resistive measurements on a recently recognized Weyl semimetal TaP under pressures up to about 100 GPa, we show the concurrence of superconductivity and a structure transition at about 70 GPa. It is found that the superconductivity becomes more pronounced when decreasing pressure and retains when the pressure is completely released. High-pressure x-ray diffraction measurements also confirm the structure phase transition from I4(1)md to P-6m2 at about 70 GPa. More importantly, ab-initial calculations reveal that the P-6m2 phase is a new Weyl semimetal phase and has only one set of Weyl points at the same energy level. Our discovery of superconductivity in TaP by high pressure will stimulate investigations on superconductivity and Majorana fermions in Weyl semimetals.

We report on the discovery of a pressure-induced topological and superconducting phase of SnSe, a material which attracts much attention recently due to its superior thermoelectric properties. In situ high-pressure electrical transport and synchrotron x-ray diffraction measurements show that the superconductivity emerges along with the formation of a CsCl-type structural phase of SnSe above around 27 GPa, with amaximum critical temperature of 3.2 K at 39 GPa. Based on ab initio calculations, this CsCl-type SnSe is predicted to be a Dirac line-node (DLN) semimetal in the absence of spin-orbit coupling, whose DLN states are protected by the coexistence of time-reversal and inversion symmetries. These results make CsCl-type SnSe an interesting model platform with simple crystal symmetry to study the interplay of topological physics and superconductivity.

We present in situ high-pressure synchrotron x-ray diffraction (XRD) and electrical transport measurements on quasi-one-dimensional single-crystal TiS3 up to 29.9-39.0 GPa in diamond-anvil cells, coupled with first-principles calculations. Counterintuitively, the conductive behavior of semiconductor TiS3 becomes increasingly insulating with pressure until P-C1 similar to 12 GPa, where extremes in all three axial ratios are observed. Upon further compression to P-C2 similar to 22 GPa, the XRD data evidence a structural phase transition. Based on our theoretical calculations, this structural transition is determined to be isosymmetric, i.e., without change of the structural symmetry (P2(1)/m), mainly resulting from rearrangement of the dangling S-2 pair along the a axis.

Topological semimetal, a novel state of quantum matter hosting exotic emergent quantum phenomena dictated by the nontrivial band topology, has emerged as a new frontier in condensed-matter physics. Very recently, the coexistence of triply degenerate points of band crossing and Weyl points near the Fermi level was theoretically predicted and experimentally identified in MoP. Via high-pressure electrical transport measurements, we report here the emergence of pressure-induced superconductivity in MoP with a critical transition temperature T-c of ca. 2.5 K at ca. 30 GPa. No structural phase transition is observed up to ca. 60 GPa via synchrotron X-ray diffraction study. Accordingly, the topologically nontrivial band protected by the crystal structure symmetries and superconductivity are expected to coexist at pressures above 30 GPa, consistent with density functional theory calculations. Thus, the pressurized MoP represents a promising candidate of topological superconductor. Our finding is expected to stimulate further exploitation of exotic emergent quantum phenomena in novel unconventional fermion system.

Tetradymite-type topological insulator Sn-doped Bp 101S0.9Te2S (Sn-BSTS), with a surface state Dirac point energy well isolated from the bulk valence and conduction bands, is an ideal platform for studying the topological transport phenomena. Here, we present high-pressure transport studies on single-crystal Sn-BSTS, combined with Raman scattering and synchrotron x-ray diffraction measurements. Over the studied pressure range of 0.7-37.2 GPa, three critical pressure points can be observed: (i) At similar to 9 GPa, a pressure-induced topological insulator-to-metal transition is revealed due to closure of the bulk band gap, which is accompanied by changes in slope of the Raman frequencies and a minimum in da within the pristine rhombohedral structure (R-3m); (ii) at similar to 13 GPa, superconductivity is observed to emerge, along with the R-3m to a C2/c (monoclinic) structural transition; (iii) at similar to 24 GPa, the superconducting transition onset temperature T-c reaches a maximum of similar to 12K, accompanied by a second structural transition from the C2/c to a body-centered cubic Im -3m phase.

Estimation of daily downward shortwave radiation (DSR) is of great importance in global energy budget and climatic modeling. The combination of satellite-based instantaneous measurements and temporal extrapolation models is the most feasible way to capture daily radiation variations at large scales. However, previous studies did not pay enough attention to topographic effects and simple temporal extrapolation methods were applied directly to rugged terrains which cover a large amount of the land surface. This paper, divided into two parts, aims at analyzing the topographic uncertainties of existing models and proposing a better method based on a mountain radiative transfer (MRT) model to calculate daily DSR. As the first part, this paper analyze the spatiotemporal variations of DSR influenced by topographic effects and checks the applicability of three temporal extrapolation methods on cloud-free days. Considering that clouds also have a strong influence on solar radiation, cloud-free days are chosen for targeted analysis of topographic effects on DSR. Three indices, the coefficient of variation, entropy-based dispersion coefficient (CH), and sill of semivariogram, are put forward to give a quantitative description of spatial heterogeneity. Our results show that the topography can dramatically strengthen the spatial heterogeneity of DSR. The index, CH, has an advantage for quantifying spatial heterogeneity as it offers a tradeoff between accuracy and efficiency. Spatial heterogeneity distorts the daily variation of DSR. Application of extrapolation methods in rugged terrains leads to overestimation of daily average DSR up to 60 W/m2 and a maximum 200 W/m2 error of instantaneous DSR on cloud-free days. This paper makes a quantitative analysis of topographic effects under different spatiotemporal conditions, which lays the foundation for developing a new extrapolation method.

Band engineering in layered metal dichalcogenides leads to a variety of physical phenomena and has obtained considerable attention recently. In this work, pressure-induced metallization and superconductivity in pristine 1T-SnSe2 is reported via electrical transport and synchrotron X-ray diffraction experiments. Electrical transport results show that the metallization emerges above 15.2 GPa followed by appearance of superconducting transition at 18.6 GPa. The superconductivity is robust with a nearly constant T-c approximate to 6.1 K between 30.1 and 50.3 GPa. High-pressure synchrotron X-ray diffraction experiments indicate that the 1T-SnSe2 phase maintains up to 46.0 GPa. Although the theoretical predicted structural transition and decomposition of SnSe2 into Sn3Se4 and Se are not detected, it is argued that the structural instability under high pressure might be crucial for the superconductivity. These findings demonstrate that 1T-SnSe2 is a very rare system from which superconductivity can be driven via multiple ways.

Noncentrosymmetric molybdenum nitride Rh2Mo3N is a conventional s-wave superconductor at ambient pressure. Here we report the evolution of structural and electronic properties of Rh2Mo3N under high pressure. X-ray diffraction measurements reveal the stability of pristine beta-Mn-type cubic structure up to 47.9 GPa, accompanied by the continuously enhanced distortion of Mo6N octahedra. Electronic transport experiments show the robustness of superconductivity under pressure, i.e., the superconducting transition temperature T-c varies only similar to 0.7 K upon compression up to 38.5 GPa. Meanwhile, detailed analyses of both structural and transport results consistently reveal a critical pressure of similar to 14.0 GPa. In agreement with the enhancement of octahedral distortion, the temperature dependence of upper critical magnetic field accords with a p-wave model at 22.0 GPa and an s-wave model at 6.0 GPa. These results suggest the emergence of novel superconductivity in the distorted Rh2Mo3N cubic phase under pressure, which could be attributed to the enhanced strength of antisymmetric spin-orbit coupling (ASOC) via pressure-modified local octahedral distortion. Our findings may shed light on the searching and understanding of unique triplet-pairing superconductivity in other inversion-broken superconductors with strong ASOC.

Surface ozone (O-3) pollution events are becoming more frequent and have recently emerged as a severe air pollution problem in China. However, the spatial-temporal distribution of surface O-3, as well as its primary synoptic and meteorological drivers, remains poorly understood. The purpose of this study was to identify the key synoptic and meteorological drivers of O-3 pollution in different regions of China. To achieve this goal, this study established meteorology overlaps of regional O-3 pollution events in space and time and applied a comprehensive statistical model selection method for optimal synoptic and meteorological models, based on a newly released O-3 dataset for 2015-2018. It was observed that extreme regional O-3 pollution events (duration >7 d) occurred more frequently and exhibited a high co-occurrence frequency (>50%) with air stagnation (AS). Moreover, the beginning and end of 69% of the regional O-3 pollution events coincided with regional daily maximum temperature changes. The intensity of AS is the dominant driver of O-3 pollution event intensity across most of the six selected megacity regions. Although other meteorological drivers, such as the intensity of hot days (HD) and meridional wind of 10 m were also important, their impacts varied according to the region. Overall, increase in extreme AS and HD led to the worsening of regional O-3 pollution events. These findings imply that mitigating regional O-3 pollution should consider changing synoptic and meteorological conditions.