Christoph Johannes Sahle

Super-oxidized porous carbon (SOPC) synthesized starting from spruce cones is demonstrated as an efficient sorbent for two lanthanide elements (Ce and Yb) from their nitrate solutions.

Spin-orbit coupling locks spin direction and spatial orientation and generates, in semi-classical magnets, a local spin easy-axis and associated ordering. Quantum spin-1/2’s defy this fate: rather than spins becoming locally anisotropic, the spin-spin interactions do. Consequently interactions become dependent on the spatial orientation of bonds between spins, prime theoretical examples of which are Kitaev magnets. Bond-directional interactions imply the existence of bond-directional magnetic modes, spin excitations that render crystallographically equivalent bonds magnetically inequivalent, which yet have remained elusive experimentally. Here we show that resonant inelastic X-ray scattering allows us to explicitly probe the bond-directional character of magnetic excitations. To do so, we use a scattering plane spanned by one bond and the corresponding spin component and scan a range of momentum transfer that encompasses multiple Brillouin zones. Applying this approach to Na ₂ IrO ₃ we establish the different bond-directional characters of magnetic excitations at ~10 meV and ~45 meV. The bond-directional nearest-neighbor excitations are a fingerprint of the dominant Kitaev interactions and even prevail in the magnetically ordered state.

We probe the spectrum of elementary excitations in SrIrO 3 by using heterostructured [ ( SrIrO 3 ) m / ( SrTiO 3 ) l ] samples to approach the bulk limit. Our resonant inelastic x-ray scattering (RIXS) measurements at the Ir L 3 edge reveal a robust low-lying collective magnetic mode with an antiferromagnetic (AFM) dispersion similar to the insulators Sr 2 IrO 4 and Sr 3 Ir 2 O 7 , albeit with a large gap and much larger linewidth. At higher energies we find the spin-orbit exciton, also strongly broadened, but with an inverted dispersion and doubled periodicity that are controlled by the charge hopping. These results demonstrate that the AFM paramagnon persists, somewhat counterintuitively, far into the metallic regime of the insulator-metal transition driven by the degree of confinement in the heterostructure. We conclude that these two excitations, which are contrasting but coexisting hallmarks of strong AFM pseudospin and charge fluctuations in a spin-orbit-coupled Mott-Slater material, are properties intrinsic to the ground state of semimetallic perovskite SrIrO 3 .

State-of-the-art spectral imaging techniques using high-brilliance sources face an inherent trade-off between signal intensity and sample integrity, particularly in hyperspectral and multispectral imaging. Traditionally, optimizing acquisition parameters, such as source wavelength, intensity, and exposure time, relies on empirical adjustments to enhance image contrast. Here, we introduce a digital twin methodology to overcome these limitations. Focusing on x-ray Raman imaging, a powerful yet underutilized speciation probe constrained by low quantum efficiency, we demonstrate its application to sensitive organic samples. Our approach enabled a 10-fold reduction in acquisition time while maintaining operation below the damage threshold, paving the way for high-fidelity spectral imaging with minimal sample degradation.

Understanding the structural and electronic properties of oxygen in materials is critical for advancing various technological applications, particularly in catalysis and energy storage. Oxygen species play a pivotal role in mediating reactions within metal-oxide systems, significantly influencing the reactivity and stability of catalysts. Insight into the electronic structure of oxygen, comprising hybridization and bonding with transition metals, provides a deeper understanding of catalytic processes and the efficiency of electrocatalysts. Additionally, oxygen's involvement in electrochemical processes within batteries, particularly through anionic redox reactions, underscores its importance in developing efficient energy storage solutions. This review focuses on the use of two empirical parameters in O K-edge simulations, offering a guide on simulating observed O spectra for solid oxides. By bridging experimental fingerprints with theoretical approaches, an in-depth understanding of the spectra is provided. First, the theory defining the empirical parameters of the FDMNES code, "dilatorb" and "screening," is presented. Then, the importance of studying the O K-edge is highlighted through a discussion of selected case studies. This highlights the essential role of oxygen K-edge experiments and simulations in advancing the understanding of catalytic and energy storage processes. By providing detailed insights into the electronic structure, bonding, and real-time transformations in (electro)catalysts, these techniques make significant contributions to material design and optimization.

Spontaneous parametric down-conversion (PDC) of photons is a gateway into the quantum realm – thoroughly studied in nonlinear optics and ubiquitously used to generate non-classical states of light. Extending PDC from the visible regime towards shorter wavelengths further enables microscopic resolution of electronic structure and quantum-enhanced X-ray detection, but remained challenging due to the process’ inherently low conversion rate. Here, we resolve the full signal cone of non-degenerate down-conversion at X-ray wavelengths and identify imprints of a polariton in the extreme ultraviolet (EUV) regime. We confirm our finding of the EUV-polariton with theoretical simulations and establish that our approach directly images the characteristic anti-crossing of polaritonic dispersion branches. This insight could open a pathway to explore strong-coupling phenomena of EUV-light-matter interaction.