In stark contrast to ordinary metals, in materials in which electrons strongly interact with each other or with phonons, electron transport is thought to resemble the flow of viscous fluids. Despite their differences, it is predicted that transport in both conventional and correlated materials is fundamentally limited by the uncertainty principle applied to energy dissipation. Here we report the observation of experimental signatures of hydrodynamic electron flow in the Weyl semimetal tungsten diphosphide. Using thermal and magneto-electric transport experiments, we find indications of the transition from a conventional metallic state at higher temperatures to a hydrodynamic electron fluid below 20 K. The hydrodynamic regime is characterized by a viscosity-induced dependence of the electrical resistivity on the sample width and by a strong violation of the Wiedemann–Franz law. Following the uncertainty principle, both electrical and thermal transport are bound by the quantum indeterminacy, independent of the underlying transport regime.

The discovery of topological materials has provided new opportunities to exploit advanced materials for heat-to-electricity energy conversion as they share many common characteristics with thermoelectric materials.In this work, we report the magneto-thermoelectric properties and Nernst effect of the topological Weyl semimetal NbP. We find that polycrystalline, bulk NbP shows a significantly larger Nernst thermopower than its conventional thermopower under magnetic field. As a result, a maximum Nernst power factor of B35 Â 10 À4 W m À1 K À2 is achieved at 9 T and 136 K, which is 4 times higher than its conventional power factor and is also comparable to that of state-of-the-art thermoelectrics. Moreover, the Nernst power factor maintains relatively large value over a broad temperature range. These results highlight that the enhancement of thermoelectric performance can be achieved in topological semimetals based on the Nernst effect and transverse transport.

for the design of highly active catalysts is the identification of the origin of the activity. However, this remains a challenge. [8,9] The activity of a given catalyst is traditionally associated with the properties of its surfaces. Thus, materials with large surface areas, good conductivity, and high mobility are understood to be good catalysts, as they have abundant active sites that favor the adsorption of intermediates and electron transfer in redox reactions. This is the motivation for widely used catalyst synthesis strategies such as nanostructuring, doping, alloying, or adding defects. Each method aims to either expose preferential crystal surfaces or engineer them to make them more active. [10][11][12] However, it is still a formidable task to locate the position of active sites rapidly and precisely from the design perspective, making the discovery of high-performance catalysts from the many potentially interesting materials a challenge.Topological materials have robust surface states and massless electrons with high mobilities. [13][14][15] Moreover, many state-of-the-art catalysts (such as Pt, Pd, Cu, Au, IrO 2 , and RuO 2 ) are understood, either from theory or experiment, to have topologically derived surface states (TSSs). [16,17] Thus, there is some evidence for the important role of TSSs in catalytic reactions. [18,19] Such states are mainly composed of The discovery of new catalysts that are efficient and sustainable is a major research endeavor for many industrial chemical processes. This requires an understanding and determination of the catalytic origins, which remains a challenge. Here, a novel method to identify the position of active sites based on searching for crystalline symmetry-protected obstructed atomic insulators (OAIs) that have metallic surface states is described. The obstructed Wannier charge centers (OWCCs) in OAIs are pinned by symmetries at some empty Wyckoff positions so that surfaces that accommodate these sites are guaranteed to have metallic obstructed surface states (OSSs). It is proposed and confirmed that the OSSs are the catalytic activity origins for crystalline materials. The theory on 2H-MoTe 2 , 1T′-MoTe 2 , and NiPS 3 bulk single crystals is verified, whose active sites are consistent with the calculations. Most importantly, several high-efficiency catalysts are successfully identified just by considering the number of OWCCs and the symmetry. Using the real-spaceinvariant theory applied to a database of 34 013 topologically trivial insulators, 1788 unique OAIs are identified, of which 465 are potential high-performance catalysts. The new methodology will facilitate and accelerate the discovery of new catalysts for a wide range of heterogeneous redox reactions.

The discovery of Weyl and Dirac fermions in solid systems is a recent major breakthrough in the field of condensed matter physics. These materials exhibit extraordinary properties in terms of carrier mobility and magnetoresistance (MR). These two quantities are highly dependent in the Weyl semimetal transition monopnictide family, i.e. NbP, TaP, NbAs, and TaAs. Furthermore, the gathered mobility and MR (or slope of MR) at 2 K in 9 T of other well-known Weyl and Dirac semimetals follow a relation similar to the right turn symbol, i.e. the MR increases rapidly with mobility; thereafter it begins to saturate after reaching a value of 10 3 . This suggests a nonlinear dependency. Nevertheless, for materials possessing high carrier mobility, it is valid to expect high MR.

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