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The excitation of coherent phonons provides unique capabilities to control fundamental properties of quantum materials on ultrafast time scales. Recently, it was predicted that a topologically protected Weyl semimetal phase in the transition metal dichalcogenide Td -WTe 2 can be controlled and, ultimately, be destroyed upon the coherent excitation of an interlayer shear mode. By monitoring electronic structure changes with femtosecond resolution, we provide here direct experimental evidence that the shear mode acts on the electronic states near the phase-defining Weyl points. Furthermore, we observe a periodic reduction in the spin splitting of bands, a distinct electronic signature of the Weyl phase-stabilizing non-centrosymmetric Td ground state of WTe 2 . The comparison with higher-frequency coherent phonon modes finally proves the shear mode-selectivity of the observed changes in the electronic structure. Our real-time observations reveal direct experimental insights into electronic processes that are of vital importance for a coherent phonon-induced topological phase transition in  Td -WTe 2 . It is predicted that topological phase transitions in quantum materials can be triggered by selective excitation of coherent phonons. Upon excitation of a shear mode, Hein et al. observe distinct perturbations of electronic Weyl semimetal fingerprints in Td -WTe 2 .

Topological physics and strong electron–electron correlations in quantum materials are typically studied independently. However, there have been rapid recent developments in quantum materials in which topological phase transitions emerge when the single-particle band structure is modified by strong interactions. Here we demonstrate that the room-temperature phase of (TaSe4)2I is a Weyl semimetal with 24 pairs of Weyl nodes. Owing to its quasi-one-dimensional structure, (TaSe4)2I also hosts an established charge-density wave instability just below room temperature. We show that the charge-density wave in (TaSe4)2I couples the bulk Weyl points and opens a bandgap. The correlation-driven topological phase transition in (TaSe4)2I provides a route towards observing condensed-matter realizations of axion electrodynamics in the gapped regime, topological chiral response effects in the semimetallic phase, and represents an avenue for exploring the interplay of correlations and topology in a solid-state material.Strong electron–electron interactions create a charge-density wave that modifies the topological state of the Weyl semimetal (TaSe4)2I. This implies the possibility of experimentally simulating axion electrodynamics in a solid-state material.

Dual topological materials are unique topological phases that host coexisting surface states of different topological nature on the same or on different material facets. Here, we show that Bi 2 TeI is a dual topological insulator. It exhibits band inversions at two time reversal symmetry points of the bulk band, which classify it as a weak topological insulator with metallic states on its ‘side’ surfaces. The mirror symmetry of the crystal structure concurrently classifies it as a topological crystalline insulator. We investigated Bi 2 TeI spectroscopically to show the existence of both two-dimensional Dirac surface states, which are susceptible to mirror symmetry breaking, and one-dimensional channels that reside along the step edges. Their mutual coexistence on the step edge, where both facets join, is facilitated by momentum and energy segregation. Our observation of a dual topological insulator should stimulate investigations of other dual topology classes with distinct surface manifestations coexisting at their boundaries. Bi 2 TeI is identified as a dual topological insulator. It is a weak topological insulator with metallic states at the (010) surfaces and a topological crystalline insulator at the (001) surfaces.

Transition metal dichalcogenides have attracted research interest over the last few decades due to their interesting structural chemistry, unusual electronic properties, rich intercalation chemistry and wide spectrum of potential applications. Despite the fact that the majority of related research focuses on semiconducting transition-metal dichalcogenides (for example, MoS 2 ), recently discovered unexpected properties of WTe 2 are provoking strong interest in semimetallic transition metal dichalcogenides featuring large magnetoresistance, pressure-driven superconductivity and Weyl semimetal states. We investigate the sister compound of WTe 2 , MoTe 2 , predicted to be a Weyl semimetal and a quantum spin Hall insulator in bulk and monolayer form, respectively. We find that bulk MoTe 2 exhibits superconductivity with a transition temperature of 0.10 K. Application of external pressure dramatically enhances the transition temperature up to maximum value of 8.2 K at 11.7 GPa. The observed dome-shaped superconductivity phase diagram provides insights into the interplay between superconductivity and topological physics. Materials which simultaneously exhibit superconductivity and topologically non-trivial electronic band structure possess potential applications in quantum computing but have yet to be found. Here, the authors find superconductivity in MoTe 2 , a material predicted to be topologically non-trivial.

By breaking the restrictions on traditional alloying strategy, the high entropy concept has promoted the exploration of the central area of phase space, thus broadening the horizon of alloy exploitation. This review highlights the marriage of the high entropy concept and van der Waals systems to form a new family of materials category, namely the high entropy van der Waals materials (HEX, HE = high entropy, X = anion clusters) and describes the current issues and next challenges. The design strategy for HEX has integrated the local feature (e.g., composition, spin, and valence states) of structural units in high entropy materials and the holistic degrees of freedom (e.g., stacking, twisting, and intercalating species) in van der Waals materials, and is successfully used for the discovery of high entropy dichalcogenides, phosphorus tri‐chalcogenides, halogens, and MXene. The rich combination and random distribution of the multiple metallic constituents on the nearly regular 2D lattice give rise to a flexible platform to study the correlation features behind a range of selected physical properties, e.g., superconductivity, magnetism, and metal–insulator transition. The deliberate design of structural units and their stacking configuration can also create novel catalysts to enhance their performance in a bunch of chemical reactions. Combining the multiple degrees of freedom inherited from both high entropy systems and van der Waals materials, high entropy van der Waals materials bring about rich emergent physical behavior (superconductivity, thermoelectricity, etc.) and excellent chemical performance (corrosion resistance, heterogenous catalysis, etc.) and is promising for further device applications.

The tunability of reaction pathways is required for exploring efficient and low cost catalysts for ammonia synthesis. There is an obstacle by the limitations arising from scaling relation for this purpose. Here, we demonstrate that the alkali earth imides ( Ae NH) combined with transition metal (TM = Fe, Co and Ni) catalysts can overcome this difficulty by utilizing functionalities arising from concerted role of active defects on the support surface and loaded transition metals. These catalysts enable ammonia production through multiple reaction pathways. The reaction rate of Co/SrNH is as high as 1686.7 mmol·g Co −1 ·h −1 and the TOFs reaches above 500 h −1 at 400 °C and 0.9 MPa, outperforming other reported Co-based catalysts as well as the benchmark Cs-Ru/MgO catalyst and industrial wüstite-based Fe catalyst under the same reaction conditions. Experimental and theoretical results show that the synergistic effect of nitrogen affinity of 3d TMs and in-situ formed NH 2− vacancy of alkali earth imides regulate the reaction pathways of the ammonia production, resulting in distinct catalytic performance different from 3d TMs. It was thus demonstrated that the appropriate combination of metal and support is essential for controlling the reaction pathway and realizing highly active and low cost catalysts for ammonia synthesis. The presence of electrically active defects on the surface of the support has been shown to be effective for N 2 activation. Here the authors discover that electron-rich polyanionic NH 2− defect allows for efficient ammonia synthesis via multiple reaction pathway by incorporating various affordable transition metals.

Topological quantum materials with kagome lattice have become the emerging frontier in the context of condensed matter physics. Kagome lattice harbors strong magnetic frustration and topological electronic states generated by the unique geometric configuration. Kagome lattice has the peculiar advantages in the aspects of magnetism, topology as well as strong correlation when the spin, charge, or orbit degrees of free is introduced, and providing a promising platform for investigating the entangled interactions among them. In this paper, we will systematically introduce the research progress on the kagome topological materials and give a perspective in the framework of the potential future development directions in this field.

Ruthenium-bearing intermetallics (Ru-IMCs) featured with well-defined structures and variable compositions offer new opportunities to develop ammonia synthesis catalysts under mild conditions. However, their complex phase nature and the numerous controlling parameters pose major challenges for catalyst design and exploration. Herein, we demonstrate that a combination of machine learning (ML) and model mining techniques can effectively address these challenges. Based on the combination techniques, we generate a two-dimensional activity volcano plot with adsorption energies of N 2 and N, and identify the radius of atom coordinating to Ru as a key parameter. The well-designed Sc 1/8 Nd 7/8 Ru 2 reaches as high as 8.18 mmol m −2 h −1 at 0.1 MPa and 400 °C. Density functional theory (DFT) calculations combined with N 2 -TPD and FT-IR studies reveal that Ru‒N interaction is controlled by the d - p orbital hybridization between Ru and N. These findings underscore the importance of ML towards material design on exploring IMCs for ammonia synthesis. Developing Ru-intermetallic catalysts for mild ammonia synthesis faces structural complexity. Here, machine learning identified Sc 1/8 Nd 7/8 Ru 2 , optimizing Ru–N bonding and orbital hybridization, enhancing catalytic activity under mild conditions.

Kagome materials have been reported to possess abundant and peculiar physical properties, which provide an excellent platform to explore exotic quantum states. We present a discovery of superconductivity in van der Waals material Pd3P2S8 composed of Pd kagome lattice under pressure. Pd3P2S8 displays superconductivity for those pressures where the semiconducting-like temperature dependence of the resistivity turns into a metallic one. Moreover, it is found that the increased pressure results in a gradual enhancement of superconducting transition temperature, which finally reaches 6.83 K at 79.5 GPa. Combining high-pressure x-ray diffraction, Raman spectroscopy and theoretical calculations, our results demonstrate that the observed superconductivity induced by high pressure in Pd3P2S8 is closely related to the formation of amorphous phase, which results from the structural instability due to the enhanced coupling between interlayer Pd and S atoms upon compression.

Superconductivity and topological quantum states are two frontier fields of research in modern condensed matter physics. The realization of superconductivity in topological materials is highly desired; however, superconductivity in such materials is typically limited to two-dimensional or three-dimensional materials and is far from being thoroughly investigated. In this work, we boost the electronic properties of the quasi-one-dimensional topological insulator bismuth iodide β-Bi 4 I 4 by applying high pressure. Superconductivity is observed in β-Bi 4 I 4 for pressures, where the temperature dependence of the resistivity changes from a semiconducting-like behavior to that of a normal metal. The superconducting transition temperature T c increases with applied pressure and reaches a maximum value of 6 K at 23 GPa, followed by a slow decrease. Our theoretical calculations suggest the presence of multiple pressure-induced topological quantum phase transitions as well as a structural–electronic instability. Topological insulators: pressure induces superconductivity Pressure-induced superconductivity is observed in topological insulator β-Bi 4 I 4 , and multiple topological phase transitions are predicted from ab initio calculations. An international team led by Binghai Yan and Claudia Felser from Max Planck Institute for Chemical Physics of Solids in Germany investigated the high-pressure behavior of the quasi-one-dimensional topological insulator β-Bi 4 I 4 . The resistivity under pressure shows a semiconductor-to-metal transition, followed by zero resistivity above 17.6 GPa, indicating the emergence of superconductivity. The critical transition temperature reaches a maximum of 6 K at 23 GPa. Ab initio calculations suggest multiple topological phase transitions, which show corresponding anomalies in the pressure-dependent resistivity data. These results are helpful in making β-Bi 4 I 4 a promising candidate of possible topological superconductivity, which is a first step to quantum computation.