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Pressure can alter interatomic distances and its electrostatic interactions, exerting a profound modifying effect on electron orbitals and bonding patterns. Conventional pressure engineering relies on compressions from external sources, which raises significant challenge in precisely applying pressure on individual molecules and also consume substantial mechanical energy. Here we report ultrasmall single-layered NbSe 2 flat tubes (< 2.31 nm) created by self-pressurization during the deselenization of NbSe 3 within carbon nanotubes (CNTs). As the internal force (4–17 GPa) is three orders of magnitude larger than the shear strength between CNTs, the flat tube is locked to prevent slippage. Electrical transport measurements indicate that the large pressure within CNTs induces enhanced intermolecular electron correlations. The strictly one-dimensional NbSe 2 flat tubes harboring the Luttinger liquid (LL) state, showing a higher tunneling exponent α N b S e 2 @ C N T ≈ 0.32 than pure CNTs ( α C N T ≈ 0.22 ). This work suggests a novel chemical approach to self-pressurization for generating new material configurations and modulating electron interactions. The chemical-driven large pressure arising inside carbon nanotubes creates energetically stable, flattened, single-layered NbSe 2 nanotubes with enhanced intermolecular electronic interactions, suggesting a chemical approach to produce materials with tailored structural and electronic properties.

The recently discovered kagome metals AV 3 Sb 5 (A = Cs, Rb, K) exhibit a variety of intriguing phenomena, such as a charge density wave (CDW) with time-reversal symmetry breaking and possible unconventional superconductivity. Here, we report a rare non-monotonic evolution of the CDW temperature ( T CDW ) with the reduction of flake thickness approaching the atomic limit, and the superconducting transition temperature ( T c ) features an inverse variation with T CDW . T CDW initially decreases to a minimum value of 72 K at 27 layers and then increases abruptly, reaching a record-high value of 120 K at 5 layers. Raman scattering measurements reveal a weakened electron-phonon coupling with the reduction of sample thickness, suggesting that a crossover from electron-phonon coupling to dominantly electronic interactions could account for the non-monotonic thickness dependence of T CDW . Our work demonstrates the novel effects of dimension reduction and carrier doping on quantum states in thin flakes and provides crucial insights into the complex mechanism of the CDW order in the family of AV 3 Sb 5 kagome metals. The kagome superconductor CsV 3 Sb 5 exhibits a charge density wave (CDW) as well as superconductivity (SC). Here, the authors find that the CDW transition temperature decreases with decreasing sample thickness to 72 K at 27 atomic layers, but then unexpectedly increases to 120 K at 5 layers, an opposite trend to SC.

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 Kondo lattice, describing a grid of the local magnetic moments coupling to itinerant electrons, is a fertile ground of strongly correlated states in condensed matter physics. While the Kagome lattice has long been predicted to host Kondo physics with exotic magnetism and nontrivial topology, no experimental realization has been achieved to the best of our knowledge. Here, we report the discovery of CsCr 6 Sb 6 , a van der Waals-like Kagome Kondo lattice featuring extremely flat, isolated bands at the Fermi level that composed entirely of Cr-3d electrons. We observe heavy fermions with the effective mass over 100 times greater than those of its vanadium counterpart. We also observe Kondo insulating behavior in an ultra-low carrier density of 10 19  cm -3 and dimensionality-induced Kondo breakdown. Counterintuitively, mechanical exfoliation of the frustrated bulk reveals hidden A-type antiferromagnetism with even-odd layer-dependent anomalous Hall effect. The realization of Kondo physics in Kagome lattice opens avenues for exploring diverse quantum criticalities in a strongly-correlated frustrated system. Accessing strong correlation effects in Kagome materials remains challenging. Here, the authors realize a Kagome Kondo lattice in CsCr 6 Sb 6 exhibiting flat, isolated Kagome bands at the Fermi level.

Interlayer decoupling plays an essential role in realizing unprecedented properties in atomically thin materials, but it remains relatively unexplored in the bulk. It is unclear how to realize a large crystal that behaves as its monolayer counterpart by artificial manipulation. Here, we construct a superlattice consisting of alternating layers of NbSe 2 and highly porous hydroxide, as a proof of principle for realizing interlayer decoupling in bulk materials. In (NaOH) 0.5 NbSe 2 , the electric decoupling is manifested by an ideal 1D insulating state along the interlayer direction. Vibration decoupling is demonstrated through the absence of interlayer models in the Raman spectrum, dominant local modes in heat capacity, low interlayer coupling energy and out-of-plane thermal conductivity (0.28 W/mK at RT) that are reduced to a few percent of NbSe 2 ’s. Consequently, a drastic enhancement of CDW transition temperature (>110 K) and Pauling-breaking 2D superconductivity is observed, suggesting that the bulk crystal behaves similarly to an exfoliated NbSe 2 monolayer. Our findings provide a route to achieve intrinsic 2D properties on a large-scale without exfoliation. Interlayer decoupling plays an essential role in realizing unprecedented properties. Here, authors construct a superlattice consisting of alternating layers of NbSe2 and highly porous hydroxide, realizing interlayer decoupling and thus realizing exotic monolayer behaviors in bulk materials.

Metal‐intercalated iron selenides are a class of superconductors that have received much attention but are less understood in comparison with their FeAs‐based counterparts. Here, the controversial issues such as Fe vacancy, the real phase responsible for superconductivity, and lattice stability have been addressed based on first‐principles calculations. New insights into the distinct features in terms of carrier doping have been revealed.

The pursuit of discovering new high-temperature superconductors that diverge from the copper-based model 1 – 3 has profound implications for explaining mechanisms behind superconductivity and may also enable new applications 4 – 8 . Here our investigation shows that the application of pressure effectively suppresses the spin–charge order in trilayer nickelate La 4 Ni 3 O 10− δ single crystals, leading to the emergence of superconductivity with a maximum critical temperature ( T c ) of around 30 K at 69.0 GPa. The d.c. susceptibility measurements confirm a substantial diamagnetic response below T c , indicating the presence of bulk superconductivity with a volume fraction exceeding 80%. In the normal state, we observe a strange metal behaviour, characterized by a linear temperature-dependent resistance extending up to 300 K. Furthermore, the layer-dependent superconductivity observed hints at a unique interlayer coupling mechanism specific to nickelates, setting them apart from cuprates in this regard. Our findings provide crucial insights into the fundamental mechanisms underpinning superconductivity, while also introducing a new material platform to explore the intricate interplay between the spin–charge order, flat band structures, interlayer coupling, strange metal behaviour and high-temperature superconductivity. The application of pressure effectively suppresses the spin–charge order in trilayer nickelate La 4 Ni 3 O 10− δ single crystals, leading to the emergence of superconductivity.

are a class of superconductors that have received much attention but are less understood in comparison with their FeAs-based counterparts. Here, the controversial issues such as Fe vacancy, the real phase responsible for superconductivity, and lattice stability have been addressed based on first-principles calculations. New insights into the distinct features in terms of carrier doping have been revealed.

Hydrogen bonds profoundly influence the fundamental chemical, physical and biological properties of molecules and materials. Owing to their relatively weaker interactions compared to other chemical bonds, hydrogen bonds alone are generally insufficient to induce substantial changes in electrical properties, thus imposing severe constraints on their applications in related devices. Here we report a metal–insulator transition controlled by hydrogen bonds for an organic–inorganic (1,3-diaminopropane) 0.5 SnSe 2 superlattice that exhibits a colossal on–off ratio of 10 7 in electrical resistivity. The key to inducing the transition is a change in the amino group’s hydrogen-bonding structure from dynamic to static. In the dynamic state, thermally activated free rotation continuously breaks and forms transient hydrogen bonds with adjacent Se anions. In the static state, the amino group forms three fixed-angle positions, each separated by 120°. Our findings contribute to the understanding of electrical phenomena in organic–inorganic hybrid materials and may be used for the design of future molecule-based electronic materials. Hydrogen bonds impact the chemical, physical and biological properties of molecular materials, but are rarely able to induce significant changes in electrical properties. Now a dynamic-to-static transition of hydrogen bonds in an organic–inorganic superlattice has been shown to yield a metal–insulator transition with an on–off ratio of 10 7 in electrical resistivity.

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 describe 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 has been successfully employed 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.