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We present here the first accurate determination of the exact structure of κ-(BEDT-TTF)2Cu2(CN)3. Not only did we show that the room temperature structure used over the last twenty years was incorrect, but we were also able to correctly and precisely determine it. The results of our work provide evidence that the structure presents a triclinic symmetry with two non-equivalent dimers in the unit cell, which implies a charge disproportionation between the dimers. However, structural refinement shows that the charge disproportionation is quite weak at room temperature.

VO2 undergoes a metal‐insulator transition (MIT) at ≈70 °C, which induces large variations in its electrical and wavelength‐dependent optical properties. These features make VO2 a highly sought‐after compound for optical, thermal, and neuromorphic applications. To foster the development of VO2‐based devices for the microelectronic industry, it is also imperative to integrate VO2 on silicon. However, high lattice mismatch and the formation of silicates at the interface between VO2 and Si degrade the quality and functionality of VO2 films. Moreover, VO2's polymorphic nature and stable VO phases pose integration issues. To address these challenges, the MIT of VO2 thin films integrated on Si with a complementary metal‐oxide semiconductor‐compatible HfxZr1−xO2 (HZO) buffer layer is investigated. Using in situ high‐resolution X‐ray diffraction and synchrotron far‐infrared spectroscopy, combined with multiscale atomic and electronic structure characterizations, it is demonstrated that VO2 on the HZO buffer layer exhibits an unusually low thermal hysteresis of ≈4 °C. In these results, the influence of strain on M2 phase nucleation, which controls the hysteresis, is unraveled. Notably, the rate of phase transition is symmetric and does not change for the heating and cooling cycles, implying no incorporation of defects during cycling, and highlighting the potential of an HZO buffer layer for reliable operation of VO2‐based devices. Strain disrupts the first‐order M1R phase transition in VO2, resulting in an M1M2R transition. This study not only underlines the potential of an HfxZr1−xO2 buffer layer for reliable VO2‐based devices but also correlates strain and hysteresis width to M2 phase. This analysis is enabled by complementary postmortem and in situ structural, electrical, and optical characterizations.

The bandwidth-tuned Wigner-Mott transition is an interaction-driven phase transition from a generalized Wigner crystal to a Fermi liquid. Because the transition is generally accompanied by both magnetic and charge-order instabilities, it remains unclear if a continuous Wigner-Mott transition exists. Here, we demonstrate bandwidth-tuned metal-insulator transitions at fixed fractional fillings of a MoSe 2 /WS 2 moiré superlattice. The bandwidth is controlled by an out-of-plane electric field. The dielectric response is probed optically with the 2s exciton in a remote WSe 2 sensor layer. The exciton spectral weight is negligible for the metallic state with a large negative dielectric constant. It continuously vanishes when the transition is approached from the insulating side, corresponding to a diverging dielectric constant or a ‘dielectric catastrophe’ driven by the critical charge dynamics near the transition. Our results support the scenario of continuous Wigner-Mott transitions in two-dimensional triangular lattices and stimulate future explorations of exotic quantum phases in their vicinities. The Wigner-Mott insulator is driven by extended Coulomb repulsion, rather than the on-site Coulomb repulsion of the Mott insulator. Here, the authors observe a continuous bandwidth-tuned transition between a metal and a Wigner-Mott insulator in a MoSe 2 /WS 2 moiré superlattice at fractional lattice filling.

Solid-state ion shuttles are of broad interest in electrochemical devices, nonvolatile memory, neuromorphic computing, and biomimicry utilizing synthetic membranes. Traditional design approaches are primarily based on substitutional doping of dissimilar valent cations in a solid lattice, which has inherent limits on dopant concentration and thereby ionic conductivity. Here, we demonstrate perovskite nickelates as Li-ion shuttles with simultaneous suppression of electronic transport via Mott transition. Electrochemically lithiated SmNiO₃ (Li-SNO) contains a large amount of mobile Li⁺ located in interstitial sites of the perovskite approaching one dopant ion per unit cell. A significant lattice expansion associated with interstitial doping allows for fast Li⁺ conduction with reduced activation energy. We further present a generalization of this approach with results on other rare-earth perovskite nickelates as well as dopants such as Na⁺. The results highlight the potential of quantum materials and emergent physics in design of ion conductors.

The phenomenon of Mott insulation involves the localisation of itinerant electrons due to strong local repulsion. Upon doping, a pseudogap (PG) phase emerges—marked by selective gapping of the Fermi surface without conventional symmetry breaking in spin or charge channels. A key challenge is understanding how quasiparticle breakdown in the Fermi liquid (FL) gives rise to this enigmatic state, and how it connects to both the Mott insulating and superconducting phases. Here, we develop a renormalisation-based construction of strongly correlated lattice models that captures the emergence of the PG phase and its transition to a Mott insulator. Applying a many-body tiling scheme to the fixed-point impurity model uncovers a lattice model with electron interactions and Kondo physics. At half-filling, the interplay between Kondo screening and bath charge fluctuations in the impurity model leads to FL breakdown. This reveals a PG phase characterised by a non-FL (the Mott metal) residing on nodal arcs, gapped antinodal regions of the Fermi surface, and an anomalous scaling of the electronic scattering rate with frequency. The eventual confinement of holon–doublon excitations of this exotic metal obtains a continuous transition into the Mott insulator. Our results identify the PG as a distinct long-range entangled quantum phase, and offer a new route to Mott criticality beyond the paradigm of local quantum criticality.

In powder bed fusion–electron beam melting, the alloy powder can scatter under electron beam irradiation. When this phenomenon—known as smoking—occurs, it makes the PBF-EBM process almost impossible. Therefore, avoiding smoking in EBM is an important research issue. In this study, we aimed to clarify the effects of powder bed preheating and mechanical stimulation on the suppression of smoking in the powder bed fusion–electron beam melting process. Direct current electrical resistivity and alternating current impedance spectroscopy measurements were conducted on Inconel 718 alloy powder at room temperature and elevated temperatures before and after mechanical stimulation (ball milling for 10–60 min) to investigate changes in the electrical properties of the surface oxide film, alongside X-ray photoelectron spectroscopy to identify the surface chemical composition. Smoking tests confirmed that preheating and ball milling both suppressed smoking. Furthermore, smoking did not occur after ball milling, even when the powder bed was not preheated. This is because the oxide film undergoes a dielectric–metallic transition due to the lattice strain introduced by ball milling. Our results are expected to benefit the development of the powder bed fusion–electron beam melting processes from the perspective of materials technology and optimization of the process conditions and powder properties to suppress smoking.

The Mott insulator in correlated electron systems arises from classical Coulomb repulsion between carriers to provide a powerful force for electron localization. Turning such an insulator into a metal, the so-called Mott transition, is commonly achieved by \"bandwidth\" control or \"band filling.\" However, both mechanisms deviate from the original concept of Mott, which attributes such a transition to the screening of Coulomb potential and associated lattice contraction. Here, we report a pressure-induced isostructural Mott transition in cubic perovskite PbCrO3. At the transition pressure of ∼3 GPa, PbCrO3 exhibits significant collapse in both lattice volume and Coulomb potential. Concurrent with the collapse, it transforms from a hybrid multiferroic insulator to a metal. For the first time to our knowledge, these findings validate the scenario conceived by Mott. Close to the Mott criticality at ∼300 K, fluctuations of the lattice and charge give rise to elastic anomalies and Laudau critical behaviors resembling the classic liquid-gas transition. The anomalously large lattice volume and Coulomb potential in the low-pressure insulating phase are largely associated with the ferroelectric distortion, which is substantially suppressed at high pressures, leading to the first-order phase transition without symmetry breaking.

We propose a minimal effective impurity model that captures the phenomenology of the Mott–Hubbard metal–insulator transition of the half-filled Hubbard model on the Bethe lattice in infinite dimensions as observed by dynamical mean field theory (DMFT). This involves extending the standard Anderson impurity model Hamiltonian to include an explicit Kondo coupling J , as well as a local on-site correlation U b on the conduction bath site connected directly to the impurity. For the case of attractive local bath correlations ( U b < 0 ), the extended Anderson impurity model (e-SIAM) sheds new light on several aspects of the DMFT phase diagram. For example, the T  = 0 metal-to-insulator quantum phase transition (QPT) is preceded by an excited state QPT (ESQPT) where the local moment eigenstates are emergent in the low-lying spectrum. Long-ranged fluctuations are observed near both the QPT and ESQPT, suggesting that they are the origin of the quantum critical scaling observed recently at high temperatures in DMFT simulations. The T  = 0 gapless excitations at the quantum critical point display particle-hole interconversion processes, and exhibit power-law behaviour in self-energies and two-particle correlations. These are signatures of non-Fermi liquid behaviour that emerge from the partial breakdown of the Kondo screening.

Quantum materials have tremendous potential for disruptive applications. However, scaling devices down has been challenging due to electronic inhomogeneities in many of these materials. Understanding and controlling these electronic patterns on a local scale has thus become crucial to further new applications. To address this issue, we have developed a new optical microscopy method that allows for the precise quasi-continuous filming of the insulator-to-metal transition in VO­2 with fine temperature steps. This enables us to track metal and insulator domains over thousands of images and quantify, for the first time, the local hysteresis properties of VO­2 thin films. The analysis of the maps has allowed us to quantify cycle-to-cycle reproducibility of the local transitions and reveals a positive correlation between the local insulator–metal transition temperatures T­c and the local hysteresis widths ΔTc. These maps also enable the optical selection of regions of high or low transition temperature in combination with large or nearly absent local hysteresis. These maps pave the way to understand and use stochasticity to advantage in these materials by picking on-demand transition properties, allowing the scaling down of devices such as optical switches, infrared microbolometers and spiking neural networks.

In this paper we critically discuss several examples of two-dimensional electronic systems displaying interaction-driven metal-insulator transitions of the Mott (or Wigner–Mott) type, including dilute two-dimension electron gases (2DEG) in semiconductors, Mott organic materials, as well as the recently discovered transition-metal dichalcogenide (TMD) moiré bilayers. Remarkably similar behavior is found in all these systems, which is starting to paint a robust picture of Mott criticality. Most notable, on the metallic side a resistivity maximum is observed whose temperature scale vanishes at the transition. We compare the available experimental data on these systems to three existing theoretical scenarios: spinon theory, Dynamical Mean Field Theory (DMFT) and percolation theory. We show that the DMFT and percolation pictures for Mott criticality can be distinguished by studying the origins of the resistivity maxima using an analysis of the dielectric response.