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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.

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.

The thickness dependence of the dispersion of spin waves in mesoscopic iron films is measured and found to be renormalized in the out-of-plane direction as the thickness is reduced. The results are captured by a Heisenberg model that accounts for the confinement in the out-of-plane direction through the loss of Fe bonds.

Resonant inelastic X-ray scattering can be used to measure the spin current carried by magnons in the presence of temperature gradients across a magnetic insulator.

Combining resonant inelastic X-ray scattering and photoluminescence spectroscopy, an elementary excitation in hexagonal-boron-nitride-based single-photon emitters has been demonstrated, giving rise to multiple regular harmonics that can explain the wide frequency range of these emitters.

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.

Experimental evidence for charge coupling to ferroelectric soft mode is scarce. Here, the authors find a photogenerated coherent phonon coupling to the electronic transition above the bandgap in the van der Waals ferroelectric semiconductor NbOI2.

The many strongly interacting degrees of freedom in transition metal oxides make it difficult to capture and describe the nature of their metal-insulator transitions. Li et al. show that a resonant magnetic X-ray nanoprobe gives access to local critical behavior that is difficult to detect otherwise.

Charge order has been established as a ubiquitous instability of the underdoped copper-oxide superconductors. New investigations reveal that it extends to the overdoped side of the phase diagram, a region otherwise known to host a conventional Fermi liquid state.

A new form of charge ordering is observed in a cuprate superconductor. At low doping, a fully rotationally symmetric ordering appears before becoming locked to the Cu–O bond directions at high doping. The link between charge correlations and fermiology give a perspective on the phase diagram.

Understanding the effect of the subtle interplay between strong and weak coupling regimes on the properties of quasiparticles is key to understanding unconventional superconductivity. Here, X-ray spectroscopies reveal the partially localized and itinerant magnetic character of quasiparticles in a doped iron pnictide material.

The complex interactions in spin spiral systems play an important role for the emergence of multiferroicity and topological magnetic order. Here, the authors investigate the magnetism associated with the two inequivalent Cu positions in the model system Cu2OSeO3, observing site-specific electronic structure and associated magnetic excitations.

Understanding the connection between qubit coherence and microscopic materials properties is vital for improving device performance. Here, the relaxation times of superconducting transmon qubits are found to be directly correlated with Nb film properties such as grain size and surface oxide composition.