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Ultrafast photoexcitation stabilizes new states of matter with rich out-of-equilibrium behaviours. Here, Lantzet al. report a transient non-thermal phase developing immediately after photoexcitation in V₂O₃, shedding a light on optical manipulation of strongly correlated systems.

The spatial scale over which metal–insulator transitions happen is not known, despite the importance of this phenomenon in basic and applied research. The authors show that in chromium-doped V₂O₃, with decreasing temperature, microscopic metallic domains coexist with an insulating background.

Understanding the dynamics of cuprates following photoexcitation can provide insights into the complex coupling mechanisms that underlie their exotic equilibrium behaviour. Here the authors use pump-probe reflection spectroscopy to investigate the nonequilibrium spin dynamics of Mott-insulating Nd₂CuO₄.

Doped Sr₂IrO₄ is of interest because of its close similarities to La₂CuO₄, a parent compound of the cuprates. Nelson et al. reveal the intrinsic evolution of its electronic structure with hole doping by avoiding the strong in-plane disorder introduced by previously used chemical substitutions.

Detailed knowledge of the low-energy electronic structure is required to understand the Mott insulating phase of Ca₂RuO₄. Here, Sutter et al. provide directly the experimental band structure of the paramagnetic insulating phase of Ca₂RuO₄and unveil the electronic origin of its Mott phase.

The pseudogap in cuprates is often linked to superconductivity. Now bulk evidence for a pseudogap is found in doped non-superconducting Sr₂IrO₄, revealing that pseudogaps in doped Mott insulators are not necessarily a precursor to superconductivity.

Ca₂RuO₄ is a Mott insulator that becomes a metal when a current is passed through it. Now, the changes in its electronic structure are revealed as this transition takes place.

Magnetic excitations in infinite-layer cuprates have been intensively studied. Here the authors use resonant inelastic x-ray scattering and theoretical calculations to study magnons in thin films of SrCuO₂, finding distinct magnon dispersion attributed to renormalization due to quantum fluctuations.

A major goal in the fields of ultracold quantum gases and quantum simulations is measuring the phase diagram of strongly interacting many-body systems. This has now been achieved in an optical-lattice-based quantum simulator. The simulation is validated through an ab initio comparison with large-scale numerical quantum Monte Carlo simulations.

Topological classification of interacting electronic states has emerged as an important topic recently. Wagner at al. show that the momentum structure of the zeros of the electron Green’s function can be used to identify a topological Mott insulator phase, similarly to the single-particle dispersion.

What makes the phonons in cuprates become chiral, as measured by their thermal Hall effect, is an unresolved question. Here, the authors rule out two extrinsic mechanisms and argue that chirality comes from a coupling of acoustic phonons to the intrinsic excitations of the CuO₂ planes.

The optimal condition for superconductivity is a long-sought issue but remains challenging. Here, Ivashko et al. demonstrate that the compressive strain to La₂CuO₄ films enhances the Coulomb and magnetic-exchange interactions relevant for superconductivity, providing a strategy to optimise the parent Mott state for superconductivity.

Irradiation with a strong terahertz electric-field pulse is found to induce a Mott transition in an organic molecular compound. The metallization is attributed to an impulsive dielectric breakdown.

Knowing whether a quantum phase transition is first- or second-order is crucial for understanding any associated exotic phenomena, but direct experimental evidence has been scarce. Here, Frandsen et al. report first-order magnetic quantum phase transitions in archetypal Mott systems, providing insight into the underlying quantum fluctuations.

Surprising observations in the evolution of electronic states in electron-doped iridates provide fresh insight into the melting of the Mott state and might lead to a fuller understanding of corresponding processes in copper-oxide superconductors.

Distinguishing band and Mott insulators experimentally represents a longstanding challenge. Here, the authors demonstrate a momentum-resolved signature of a dimerized Mott-insulator in the out-of-plane spectral function of Nb₃Br₈.

Long-range Coulomb interactions play an important role in the non-equilibrium charge dynamics of Mott insulators, but are difficult to unravel experimentally. Here, transient spectroscopy and theoretical analyses reveal Coulomb interactions stabilize biexcitons over four lattice sites in a 1D Mott insulator.

BaFe₂Se₃ is a ladder-compound that exhibits superconductivity under pressure. Using a density matrix renormalization group calculation to compare results with resonant inelastic X-ray scattering measurements, the authors conclude that this material is realized in an orbital-selective Mott phase.

Nanoscale bandgap tuning in van der Waals heterobilayers using an electro-plasmonic nanocavity provides electrical control of exciton dynamics, producing localized interlayer exciton density gradients and enhanced diffusion currents in the nanoscale.

The interplay between superconductivity, electron correlation and atomic ordering is at the heart of condensed-matter physics. Here, the authors demonstrate a link between superconductivity in the layered chalcogenide TaS_2−xSe_xand the ordering of the sulphur and selenium atoms

Bistable superlattice switching between two lattice configurations with sharply contrasting periodicities has been observed in monolayer TaIrTe₄, a dual quantum spin Hall insulator.

The electron dynamics of single-layer Bi₂Sr_2−xLa_xCuO_6+δ is studied as a function of doping, revealing the evolution of charge-transfer excitations from incoherent and localized (as in a Mott insulator) to coherent and delocalized (as in a conventional metal).

Photoinduced phase transition is a central issue in the field of non-equilibrium quantum physics. Here, the authors demonstrate that a terahertz electric-field pulse changes a Mott insulator of an organic molecular compound to a macroscopically polarized charge-order state.

Estimating the entanglement in a system is vital for quantum information processing, particularly in many-body systems. To this end, Cramer et al.experimentally quantify multi-partite entanglement in an optical lattice across the superfluid-Mott insulator phase transition and at different temperatures.

Quantifying the degree of correlation required to drive a Mott insulator transition is a crucial aspect in understanding and manipulating correlated electrons. Here, the authors introduce a thallium-based cuprate system and use resonant inelastic X-ray scattering, combined with Hubbard-Heisenberg modeling, to establish a universal relation between electron interactions and magnon dispersion, suggesting optimal superconductivity at intermediate correlation strength.

A highly nonlinear optical response can be used to time-resolve light-induced phase transitions with few-femtosecond to sub-femtosecond accuracy, paving the way for time-resolving highly correlated many-body dynamics in strongly correlated systems with few-femtosecond accuracy.

Quantitative measurements that establish the existence and evolution of quasiparticles across the whole phase diagram of a cuprate superconductor help to distinguish the many theoretical models for high-temperature superconductivity.

A near-field optical microscopy study provides nanoscale insight into an insulator-to-metal transition and the interplay with a neighbouring structural phase transition in a prototypical correlated electron material.

Strong electronic correlations in 5d materials such as osmates may combine with spin-orbit coupling to yield novel order. Here, the authors demonstrate how spin-orbit coupling in pyrochlore Cd₂Os₂O₇generates magnetic order and excitations associated with a magnetic metal-insulator transition.

Topological surface states in lead-doped tin selenide are assumed to arise from massive Dirac states in the bulk, but this has not been demonstrated to date. Using thermoelectric transport measurements, Liang et al.now close this gap, and further show a sign anomaly in the Nernst signal due to band inversion.

When electrons experience Coulomb repulsion, their kinetic energy becomes significantly reduced. This effect has now been measured in the pnictide superconductor LaFePO, and shows that correlations between electrons in these materials are just as strong as in some copper oxide and ruthenate superconductors.

The authors use time-resolved scanning near-field optical microscopy to probe the ultrafast excitonic processes and their impact on waveguide operation in transition metal dichalcogenide crystals. They observe significant modulation of the complex index by monitoring waveguide modes on the fs time scale, and identify both coherent and incoherent manipulations of WSe₂ excitonic resonances.

Magnetic insulators often display antiferromagnetic ordering owing to implications from the Pauli exclusion principle. Here, the authors predict ferromagnetism on the basis of intra-site Hund's rules in ferroelectric titanate superlattices showing charge and Jahn–Teller induced orbital orderings.

The pseudogap phase exhibited by the cuprates is almost as enigmatic as superconductivity in these materials itself. A time-resolved study performed by Cilento et al. suggests that this state can be photoexcited into a transient non-equilibrium state that is more conductive than the equilibrium state.

Topological spin textures produce versatile electronic functionalities, but are scarcely exploited for achieving heat to electricity conversion. Here, Fujishiro et al. attribute an enhanced magneto-thermopower in MnGe with topological spin hedgehogs, to electron scattering via the dynamics of an emergent magnetic field.

Solution-processable CdS ‘bulk’ nanocrystals show efficient on-chip lasing under quasi-continuous-wave conditions with excellent beam quality and pump thresholds.

Iridates are known to exhibit a range of exotic electronic and magnetic behaviours but it is difficult to prepare isolated [IrO₆]⁸⁻ species via soft chemical routes. Here, the authors isolate the isoelectronic [IrF₆]²⁻complex, and assess it as a model and for iridate analogues.