Thermoelectric technology enables the harvest of waste heat and its direct conversion into electricity. The conversion efficiency is determined by the materials figure of merit Here we show a maximum of ~2.8 ± 0.5 at 773 kelvin in n-type tin selenide (SnSe) crystals out of plane. The thermal conductivity in layered SnSe crystals is the lowest in the out-of-plane direction [two-dimensional (2D) phonon transport]. We doped SnSe with bromine to make n-type SnSe crystals with the overlapping interlayer charge density (3D charge transport). A continuous phase transition increases the symmetry and diverges two converged conduction bands. These two factors improve carrier mobility, while preserving a large Seebeck coefficient. Our findings can be applied in 2D layered materials and provide a new strategy to enhance out-of-plane electrical transport properties without degrading thermal properties.

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MnBi 2 Te 4 is an antiferromagnetic topological insulator that has stimulated intense interest due to its exotic quantum phenomena and promising device applications. The surface structure is a determinant factor to understand the magnetic and topological behavior of MnBi 2 Te 4 , yet its precise atomic structure remains elusive. Here we discovered a surface collapse and reconstruction of few-layer MnBi 2 Te 4 exfoliated under delicate protection. Instead of the ideal septuple-layer structure in the bulk, the collapsed surface is shown to reconstruct as a Mn-doped Bi 2 Te 3 quintuple layer and a Mn x Bi y Te double layer with a clear van der Waals gap in between. Combined with first-principles calculations, such surface collapse is attributed to the abundant intrinsic Mn−Bi antisite defects and the tellurium vacancy in the exfoliated surface, which is further supported by in situ annealing and electron irradiation experiments. Our results shed light on the understanding of the intricate surface-bulk correspondence of MnBi 2 Te 4 and provide an insightful perspective on the surface-related quantum measurements in MnBi 2 Te 4 few-layer devices.

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Under global warming, dry and hot events have been increasing in recent decades and are projected to increase in the future across global land areas. The impacts of compound dry and hot events may lead to increased stress to the natural and human systems than separate dry or hot events. Thus, quantitative assessments of global land areas affected by these compound events are needed to understand their risks. This study focuses on the variation in global land and cropland areas affected by compound dry and hot events for both historical and future periods using observations from Climatic Research Unit (CRU) and simulations from Coupled Model Intercomparison Project Phase 5 (CMIP5) climate models. Based on historical observations and simulations, a substantial increase in the spatial extent of these compound events was detected, especially since the 1980s. Climate model projections under the Representative Concentration Pathway (RCP) 8.5 scenario reveal that both global land and cropland areas affected by compound dry and hot events will increase to approximately 1.7-1.8 times by the end of the 21st century. Based on different thresholds of compound events, the spatial extent of global land areas during the June-July-August (December-January-February) season will increase