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Experimental studies of hydrogen at high pressure are challenging, so theory is central to understanding its phase behaviour; however, computed phase diagrams do not agree with previous measurements. Here, the authors use a quantum Monte Carlo method and present results in qualitative agreement with experiment.

Excitons dominate the optoelectronic response of many materials and exciton transport often limits the efficiency of optoelectronic devices such as solar cells or photodetectors. Using quantum geometry, the authors find that topological excitons undergo enhanced diffusion across a wide range of transport regimes.

Little was known about the properties of hydrogen under extreme pressure. Experiments now reveal key details about the arrangement of molecules in several of the element’s high-pressure phases.

Multi-gap topology is a new avenue in topological phases of matter but it remains difficult to verify in real materials. Here, the authors predict multi-gap topologies and associated phase transitions driven by braiding processes in the phonon spectra of monolayer silicates, providing clear signatures for experimental verification.

Excitons can exhibit topologically non-trivial states. Here, the authors theoretically demonstrate that excitons can exhibit controllable topology and localization properties due to their geometry in organic polymers.

Competing charge density wave states were recently reported in the bilayer Kagome metal ScV₆Sn₆, but the mechanism remained unclear. Here the authors present a microscopic theory, highlighting the crucial role of anharmonic phonon-phonon interactions, and reconcile previous experimental and theoretical reports.

A molecular design strategy for reducing the vibration-induced non-radiative losses in emissive organic semiconductors is realized by decoupling excitons from high-frequency vibrations.

Nitrogen-doped lutetium hydride, recently proposed as a superconductor at near-ambient conditions, features distinct color changes from blue to pink to red as a function of pressure. Using theoretical calculations, the authors identify the pink phase as hydrogen-deficient LuH₂ and find that this phase is not a phonon-mediated superconductor near room temperature. Further, the color is controlled by the concentration of hydrogen vacancies.

Solid helium is predicted to become a metal at extraordinarily high pressures of 25 TPa. Here, the authors predict that helium becomes an excitonic insulator just below the metallization pressure, and a superconductor just above the metallization pressure.

Here, the authors report on evidence of an excitonic species formed by electrons in high-energy conduction band states with a negative effective mass, explaining previous observations of quantum interference phenomena in two-dimensional semiconductors.

Here, the authors report on the large twist-angle susceptibility of excitons involving upper conduction bands in transition metal dichalcogenide bilayers. These high-lying excitons couple with band-edge excitons, and give rise to nonlinear quantum-optical processes that become tuneable by twisting.

Molecular understanding of water is challenging due to the structural complexity of liquid water and the large number of ice phases. Here the authors use a machine-learning potential trained on liquid water to demonstrate the structural similarity of liquid water and that of 54 real and hypothetical ice phases.

The complex coupling between charge-carriers and phonons in bismuth oxyiodide (BiOI) are uncovered, showing how carrier localisation is avoided and long transport lengths achieved. As a result, BiOI is revealed to be highly effective for X-ray detection.

Charge-carrier dynamics are fundamental to the operation and performance of semiconductor devices. In methylammonium lead iodide perovskites, carriers in the non-equilibrium regime after excitation propagate ballistically over 150 nm within 20 fs.