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The authors demonstrate the existence of chiral phonons in a non-chiral ferroelectric material, opening the possibility for phonon chirality control through ferroic switching of the electric polarization.

Using circularly polarized inelastic X-ray scattering, the authors map spin-wave (magnon) excitations in the altermagnet CrSb and detect a reversible chiral signal for the first time, establishing a practical method to probe altermagnetic magnons.

The authors study epitaxial thin films of the pyrochlore-sublattice compound LiTi2O4 by RIXS and ARPES. They observe cooperation between strong electron correlations and strong electron-phonon coupling, giving rise to a mobile polaronic ground state in which charge motion and lattice distortions are coupled.

It is known that the spin-excitation spectrum of the undoped parents of iron-pnictide superconductors contains a pronounced magnon peak, but it is unclear whether this survives doping into the superconducting state. Schmitt et al.report resonant inelastic X-ray scattering spectra that suggest it does.

Our experimental proof of chiral phonons demonstrates a degree of freedom in condensed matter that is of fundamental importance and opens the door to exploration of emergent phenomena based on chiral bosons.

In this work, authors show that O-redox in 4d and 5d transition metal oxides involves the formation of molecular oxygen trapped in the particles. These results are in accord with observations in 3d oxides and show that the greater covalency of the 4d and 5d oxides does not stabilise peroxo-like species.

Multilayer-grating-based spectrometer with high photon flux and moderate energy resolution for tender X-ray

Nickelates have been shown to host unconventional superconductivity, and recently it has been found that the choice of substrate can significantly change the superconducting critical temperature. This suggests, that like some Cuprates, strain could be important. Here Gao, Fan, Wang, and coauthors find that magnetic excitations in a parent Nickelate are insensitive to substrate choice, and therefore strain, which differs markedly from the case of Cuprates.

A major mystery in cuprate superconductors is how Cooper pairs form and condense. Here, the authors use RIXS and STM techniques to reveal that a charge-ordered insulating phase and enhanced bond-buckling phonons play important roles in this process.

Unconventional superconductivity is often associated with the presence of other kinds of electronic order. Observations of charge order in infinite-layer nickelate superconductors show that they fit this pattern.

It was recently found that a certain nickelate compound, La₃Ni₂O₇, at moderately high pressures has a superconducting phase that persists to above liquid nitrogen temperatures. Here, by studying the parent phase at ambient pressure, Chen et al uncover rich magnetic properties and show the vital role of the strong bonding of the inter-layer Ni orbitals in the magnetic and electronic excitations.

It has been suggested that the strange metal phase in cuprates stems from a quantum critical point slightly above optimal doping. By resonant x-ray scattering in two cuprate families in a wide doping range, Arpaia et al. show that charge density fluctuations could be associated with this quantum critical point.

In optimally doped Nd_0.8Sr_0.2NiO₂H epitaxial film, combined state-of-the-art experimental and theoretical approaches show abundant hydrogen with zero resistivity, and its critical role in superconductivity in epitaxial infinite-layer nickelates.

Magnonics aims to use the collective excitations of spins in magnetic materials, magnons, for information transfer and processing. In this manuscript, Elnaggar et al. study magnon excitations in hematite using resonant inelastic X-ray scattering, observing higher-order magnons.

Multipolar magnetic excitations are challenging to measure as most experimental probes are sensitive to dipolar processes. Here, Nag et al. show the existence of dispersing quadrupolar components to the spin excitations in an antiferromagnet, highlighting the importance of higher order magnetic excitations.

In flat band materials, the ’flat’ dispersion of the electronic states mean that interactions between electrons can be strong, potentially leading to a variety of interesting magnetic and transport properties. Here, Nag et al study the Kagomé semimetal Co3Sn2S2, and show a nearly flat Stoner excitation dispersion, a clear indication of spin-polarized and flat electronic bands.

Denoising low-counting statistics data in the presence of multiple, unknown noise profiles is a challenging task in scientific applications where high accuracy is required. Oppliger and colleagues train a deep convolutional neural network on pairs of experimental low- and high-noise X-ray diffraction data and demonstrate better performance on experimental noise filtering compared with the case of training on artificial data pairs.

Oxygen redox cathodes deliver higher energy densities than those based on transition metal redox but commonly exhibit voltage fade on extended cycling. The loss of O-redox capacity and voltage fade is shown to arise from a reduction in O²⁻/O₂ redox process reversibility and O₂ loss.

The mechanism of oxygen redox in high-energy transition metal oxide cathodes is elusive. Here the authors illustrate the nature of the electron-hole states on oxide ions, offering insights for realizing reversible, high-voltage cathodes.

In transition metal oxides, an insulating band gap is found when the energy scales related to ionic charge excitations dominate over electronic itinerancy. Here, the authors demonstrate strong electron-phonon interactions in Li₂CuO₂and their effect on the insulating band gap.

Here, Pelliciari et al. present resonant inelastic X-ray scattering on monolayer samples of unconventional superconductor FeSe, finding evidence for gapped and dispersionless spin excitations. These experiments are very difficult due to the extremely small scattering volume of the FeSe monolayer.

Understanding the severe voltage hysteresis in the first cycle of Li-rich cathodes is essential to realize their full potential in batteries. P. G. Bruce and colleagues report the formation of molecular O₂ on charging rather than other oxidized O species is the cause for the voltage hysteresis.

A spin–orbit-entangled exciton state in the van der Waals material NiPS₃ is observed, and found to arise from many-body states of a Zhang–Rice singlet.

In oxygen-redox intercalation cathodes, voltage hysteresis can be avoided by forming cathode materials with a ‘ribbon’ superstructure in the transition metal layers that suppresses transition metal migration.

The authors present evidence for the formation of commensurate charge order in non-superconducting thin films of infinite-layer nickelates, whereas they find no charge order in a superconducting film.

X-ray scattering experiments show that the quantum fluctuations associated with charge order take a form that is incompatible with the idea of competition between charge order and superconductivity.

Element-specific electronic properties can be probed using resonant inelastic X-ray scattering (RIXS). A combination of X-ray absorption and emission, RIXS can investigate collective excitations in energy and momentum space. This Primer explores both valence and core RIXS, including background theory, experimental set-up, data analysis and example applications.

Spin orbit coupling (SOC) is a feature crucial to many interesting physics phenomena ranging from Mott insulators to topological insulators. Here, the authors use resonant inelastic X-ray scattering to study the low-energy excitations of the Mott insulator, Ca2RuO4, and reveal the orbital character of the magnetic properties of the system.

Frustration in magnetic systems may lead to exotic quantum phases such as spin liquid and spin ice state. Here the authors demonstrate that compressive epitaxial strain in La₂NiO₄ films deposited on different substrates can tune antiferromagnetic exchange interactions and increase the degree of frustration through the increased level of incompatibility between exchange interactions.