_{3}has emerged as an important model system for Kitaev physics in solids. We have used resonant inelastic x-ray scattering with our new IRIXS spectrometer to determine the exchange interactions in RuCl

_{3}, which can now serve as the basis for theoretical work on this system. Since IRIXS only requires micrometer-sized crystals, our approach has the potential to evolve into a powerful screening tool for the rapidly expanding list of spin-liquid candidate materials. more

_{2}Cu

_{3}O

_{(6.67)}under highly homogeneous uniaxial pressure and demonstrated the power of this method to modulate the interplay between superconducting and charge-density-wave (CDW) phases without introducing disorder and inhomogeneity. Specifically, he showed that uniaxial pressure enhances short-range-ordered CDWs in the copper-oxide planes and confirmed that the underlying order parameter is uniaxial, thus conclusively resolving a long-standing debate (H.H. Kim et al., Phys. Rev. Lett. 126, 037002 (2021) more

*T*

_{c}superconducting cuprates. We combined uniaxial strain with resonant x-ray scattering (RXS) to explore a segment of the phase space of correlated electrons in the cuprates that had previously been inaccessible. Our findings clarify the nature of the CDW while demonstrating that the combination of uniaxial strain and RXS can become a powerful tool to shine light onto the complex interplay of electronic correlations in quantum materials. more

_{3}) have been the subject of intense investigation because of their rich phase diagram that comprises a sharp temperature-driven metal-to-insulator transition and an unusual antiferromagnetic ground state. Recently, we used high-resolution resonant inelastic x-ray scattering (RIXS) at the Ni L3 edge to study simultaneously the bond and magnetic orders that develop in these materials and that can be controlled via heterostructuring. Following our initial measurement of magnetic excitations in bulk-like films [1,2] we have now observed striking variations of the spin dynamics in different nickelate heterostructures and were able to explain these data in terms of a microscopic model [3]. The results show that RIXS gives valuable insights into the interplay of different collective ordering phenomena in this prototypical transition-metal oxide.

[1] Y. Lu et al., Phys. Rev. X 8, 031014 (2018)

[2] https://www.esrf.eu/home/UsersAndScience/Publications/Highlights/esrf-highlights-2018.html

[3] K. Fürsich et al., Phys. Rev. B 99, 165124 (2019) - Editors' Suggestion more

H. Suzuki, H. Gretarsson, H. Ishikawa, K. Ueda, Z. Yang, H. Liu, H. Kim, D. Kukusta, A. Yaresko, M. Minola, J. A. Sears, S. Francoual, H.-C. Wille, J. Nuss, H. Takagi, B. J. Kim, G. Khaliullin, H. Yavaş and B. Keimer,

*Nature Materials*(2019) more

_{2}IrO

_{4}, an archetypal spin-orbit Mott insulator.

"Pseudo-Jahn-Teller Effect and Magnetoelastic Coupling in Spin-Orbit Mott Insulators"

H. Liu and G. Khaliullin, Phys. Rev. Lett. 122, 057203 (2019)

"Pseudospin-lattice coupling in the spin-orbit Mott insulator Sr

_{2}IrO

_{4}"

J. Porras et al., Phys. Rev. B 99, 085125 (2019) more

Two new papers report important progress towards the goal of designing new magnetic states in oxide heterostructures. First, we used high-resolution inelastic x-ray scattering to directly determine the magnon dispersion relations and exchange interactions in an epitaxial film of NdNiO

more
_{3}[1]. We then established an elementary model system – NdNiO_{3}slabs embedded in a non-magnetic NdGaO_{3}matrix – to show that both collinear and non-collinear magnetic structures can be realized, depending on the slab thickness. [2] The crossover between both spin structures can be qualitatively understood in a low-energy spin model with the competing exchange interactions determined by RIXS. Magnetic slabs thus provide new perspectives for research on complex magnetism, in analogy to two-dimensional materials created by exfoliation. [1] Y. Lu et al., Phys. Rev. X 8, 031014 (2018) [2] M. Hepting et al., Nature Physics (2018)_{3}, we made the surprising discovery that three-dimensional charge order is present in the absence of magnetic fields, and persists to much higher temperatures than the two-dimensional order investigated in prior work. The results offer new insight into the unusual stability of charge density waves in YBCO, as well as fresh perspectives for experiments elucidating the influence of charge order on the electronic properties of cuprates without the need to apply high magnetic fields. M. Bluschke et al., Nature Comm. 9, Article number: 2978 (2018)

See also the time lapse video of him, Simon Mayer, Hasan Yavas and others assembling the spectrometer.

_{2}RuO

_{4}revealed a well-defined, dispersive "Higgs" mode that modulates the amplitude of the ordered moment. The mode quickly decays into transverse spin waves at the antiferromagnetic ordering wavevector, and through a complete mapping of the transverse modes in the reciprocal space we were able to obtain a quantitative understanding of the decay process. The results establish a novel condensed matter platform for research on the dynamics of the Higgs mode.