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  1. Abstract

    Dirac and Weyl semimetals are a central topic of contemporary condensed matter physics, and the discovery of new compounds with Dirac/Weyl electronic states is crucial to the advancement of topological materials and quantum technologies. Here we show a widely applicable strategy that uses high configuration entropy to engineer relativistic electronic states. We take theAMnSb2(A= Ba, Sr, Ca, Eu, and Yb) Dirac material family as an example and demonstrate that mixing of Ba, Sr, Ca, Eu and Yb at theAsite generates the compound (Ba0.38Sr0.14Ca0.16Eu0.16Yb0.16)MnSb2(denoted asA5MnSb2), giving access to a polar structure with a space group that is not present in any of the parent compounds.A5MnSb2is an entropy-stabilized phase that preserves its linear band dispersion despite considerable lattice disorder. Although bothA5MnSb2andAMnSb2have quasi-two-dimensional crystal structures, the two-dimensional Dirac states in the pristineAMnSb2evolve into a highly anisotropic quasi-three-dimensional Dirac state triggered by local structure distortions in the high-entropy phase, which is revealed by Shubnikov–de Haas oscillations measurements.

     
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  2. Thermal rectification is an asymmetric heat transfer process where directionally dependent transport occurs along a given axis. In this work, geometric parameters that govern thermal rectification in solids composed of various semiconducting materials were investigated utilizing metalattice data for seven materials with pore sizes ranging between 2 and 30 nm. Using numerical simulation, thermal rectification was calculated at different thermal biases in single material systems, including silicon, cubic boron nitride, and diamond, among others. The largest thermal rectification for each material was exhibited in bilayer sample stacks that were thermally matched (i.e., the thermal resistance of each layer in the stack is equal in either forward or reverse direction). Of the materials tested, diamond provided the highest thermal rectification for all cases, with its best case achieving a thermal rectification of 57.2%. This novel thermal functionality will find application in advanced applications for temperature regulation, including resonator systems where thermal effects may significantly alter and/or degrade performance. 
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  3. Oxides of p-block metals (e.g., indium oxide) and semimetals (e.g., antimony oxide) are of broad practical interest as transparent conductors and light absorbers for solar photoconversion due to the tunability of their electronic conductivity and optical absorption. Comparatively, these oxides have found limited applications in solar-to-hydrogen photocatalysis primarily due to their high electronegativity, which impedes electron transfer for converting protons into molecular hydrogen. We have shown recently that inserting s-block metal cations into p-block oxides is effective at lowering electronegativities while affording further control of band gaps. Here, we explain the origins of this dual tunability by demonstrating the mediator role of s-block metal cations in modulating orbital hybridization while not contributing to frontier electronic states. From this result, we carry out a comprehensive computational study of 109 ternary oxides of s- and p-block metal elements as candidate photocatalysts for solar hydrogen generation. We downselect the most desirable materials using band gaps and band edges obtained from Hubbard-corrected density-functional theory with Hubbard parameters computed entirely from first principles, evaluate the stability of these oxides in aqueous conditions, and characterize experimentally four of the remaining materials, synthesized with high phase uniformity, to assess the accuracy of computational predictions. We thus propose seven oxide semiconductors, including CsIn3O5, Sr2In2O5, and KSbO2 which, to the extent of our literature review, have not been previously considered as water-splitting photocatalysts. 
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  4. null (Ed.)
    Tuning the work functions of materials is of practical interest for maximizing the performance of microelectronic and (photo)electrochemical devices, as the efficiency of these systems depends on the ability to control electronic levels at surfaces and across interfaces. Perovskites are promising compounds to achieve such control. In this work, we examine the work functions of more than 1000 perovskite oxide surfaces (ABO 3 ) using data-driven (machine-learning) analysis and identify the factors that determine their magnitude. While the work functions of the BO 2 -terminated surfaces are sensitive to the energy of the hybridized oxygen p bands, the work functions of the AO-terminated surfaces exhibit a much less trivial dependence with respect to the filling of the d bands of the B-site atom and of its electronic affinity. This study shows the utility of interpretable data-driven models in analyzing the work functions of cubic perovskites from a limited number of electronic-structure descriptors. 
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