Spin waves and spin-state transitions in a ruthenate high-temperature antiferromagnet.

Ruthenium compounds serve as a platform for fundamental concepts such as spin-triplet superconductivity1, Kitaev spin liquids2-5 and solid-state analogues of the Higgs mode in particle physics6,7. However, basic questions about the electronic structure of ruthenates remain unanswered, because several key parameters (including Hund's coupling, spin-orbit coupling and exchange interactions) are comparable in magnitude and their interplay is poorly understood, partly due to difficulties in synthesizing large single crystals for spectroscopic experiments. Here we introduce a resonant inelastic X-ray scattering (RIXS)8,9 technique capable of probing collective modes in microcrystals of 4d electron materials. We observe spin waves and spin-state transitions in the honeycomb antiferromagnet SrRu2O6 (ref. 10) and use the extracted exchange interactions and measured magnon gap to explain its high Néel temperature11-16. We expect that the RIXS method presented here will enable momentum-resolved spectroscopy of a large class of 4d transition-metal compounds.

4f Crystal Field Ground State of the Strongly Correlated Topological Insulator SmB_{6}.

We investigated the crystal-electric field ground state of the 4f manifold in the strongly correlated topological insulator SmB_{6} using core-level nonresonant inelastic x-ray scattering. The directional dependence of the scattering function that arises from higher multipole transitions establishes unambiguously that the Γ_{8} quartet state of the Sm f^{5} J=5/2 configuration governs the ground-state symmetry and, hence, the topological properties of SmB_{6}. Our findings contradict the results of density functional calculations reported so far.

X-ray resonant photoexcitation: linewidths and energies of Kα transitions in highly charged Fe ions.

Photoabsorption by and fluorescence of the Kα transitions in highly charged iron ions are essential mechanisms for x-ray radiation transfer in astrophysical environments. We study photoabsorption due to the main Kα transitions in highly charged iron ions from heliumlike to fluorinelike (Fe24+ to Fe17+) using monochromatic x rays around 6.6 keV at the PETRA III synchrotron photon source. Natural linewidths were determined with hitherto unattained accuracy. The observed transitions are of particular interest for the understanding of photoexcited plasmas found in x-ray binary stars and active galactic nuclei.

The effect of skeletal muscle area and attenuation in patients with sternum fracture due to blunt chest trauma.

OBJECTIVE: This study aims to retrospectively investigate the imaging features of patients with sternum fracture (SF) and concomitant organ injuries. We also aimed to evaluate the potential prognostic effect of skeletal muscle area (TMA) and muscle attenuation (MuA) values. PATIENTS AND METHODS: Computed tomography (CT) images of patients with SF were re-evaluated by two observers (Observer-1 and 2). Observer-3 has measured TMA and MuA values. Observer-1 has repeated the measurements blindly to the first measurement results to evaluate the inter-observer agreement. The length of hospital stay, death, hemiplegia, or quadriplegia were investigated from the archives. Mann-Whitney U-test or Student's t-test was used to investigate the relationship between linear variables. The intraclass correlation coefficient (ICC) score was used to evaluate the interobserver agreement. Logistic regression analysis was used to estimate the relative effect of variables by calculating unadjusted odds ratios (ORs) for categorical outcomes. RESULTS: Sixty-five patients had SF and 53 patients had SF and concomitant organ injuries. The most common injuries accompanying SF were rib fracture (73.58%) and lung contusion (60.38%). Manubrium fracture was the most common fracture location (52.3%), and 18 patients (27.7%) had displaced SF. Eight patients (15.1%) were discharged with plegia and five (9.4%) died. Hemothorax, displaced SF and decreased MuA were predictors of prolonged hospital stay, and the presence of cardiac contusion, displaced SF, hemothorax, and vertebra body fracture were independent factors for death. CONCLUSIONS: The presence of a displaced SF and decreased MuA value are important prognostic factors in patients with SF.

Proximate ferromagnetic state in the Kitaev model material α-RuCl3.

α-RuCl3 is a major candidate for the realization of the Kitaev quantum spin liquid, but its zigzag antiferromagnetic order at low temperatures indicates deviations from the Kitaev model. We have quantified the spin Hamiltonian of α-RuCl3 by a resonant inelastic x-ray scattering study at the Ru L3 absorption edge. In the paramagnetic state, the quasi-elastic intensity of magnetic excitations has a broad maximum around the zone center without any local maxima at the zigzag magnetic Bragg wavevectors. This finding implies that the zigzag order is fragile and readily destabilized by competing ferromagnetic correlations. The classical ground state of the experimentally determined Hamiltonian is actually ferromagnetic. The zigzag state is stabilized by quantum fluctuations, leaving ferromagnetism - along with the Kitaev spin liquid - as energetically proximate metastable states. The three closely competing states and their collective excitations hold the key to the theoretical understanding of the unusual properties of α-RuCl3 in magnetic fields.

Observation of phonons with resonant inelastic x-ray scattering.

Phonons, the quantum mechanical representation of lattice vibrations, and their coupling to the electronic degrees of freedom are important for understanding thermal and electric properties of materials. For the first time, phonons have been measured using resonant inelastic x-ray scattering (RIXS) across the Cu K-edge in cupric oxide (CuO). Analyzing these spectra using an ultra-short core-hole lifetime approximation and exact diagonalization techniques, we can explain the essential inelastic features. The relative spectral intensities are related to the electron-phonon coupling strengths.