Soft X-ray Resonant Inelastic X-ray Scattering Research Articles

Paramagnon dispersion in β -FeSe observed by Fe L -edge resonant inelastic x-ray scattering

We report an Fe $L$-edge resonant inelastic x-ray scattering (RIXS) study of the unusual superconductor $\beta$-FeSe. The high energy resolution of this RIXS experiment ($\approx\,$55$\,$meV FWHM) made it possible to resolve low-energy excitations of the Fe $3d$ manifold. These include a broad peak which shows dispersive trends between 100-200$\,$meV along the $(\pi,0)$ and $(\pi,\pi)$ directions of the one-Fe square reciprocal lattice, and which can be attributed to paramagnon excitations. The multi-band valence state of FeSe is among the most metallic in which such excitations have been discerned by soft x-ray RIXS.

Three-dimensional dispersion of spin waves measured in NiO by resonant inelastic x-ray scattering

The authors have investigated the dispersion of magnetic excitations in thin films of antiferromagnetic NiO using resonant inelastic x-ray scattering (RIXS) at the ${L}_{3}$ edge of nickel. They demonstrate here that, thanks to the recent improvements in energy resolution and scattering geometry, soft x-ray RIXS is a valid complement to inelastic neutron scattering in this field because it allows a clear identification of the spin-wave peaks not only in bulk crystals but also in thin films and heterostructures too small for neutron studies. Moreover, the spin-wave dispersion measured along three high-symmetry directions of the 3D fcc Brillouin zone allows an accurate determination of the main super-exchange integral ${J}^{\ensuremath{'}}$ that establishes the antiferromagnetic structure of NiO. This report demonstrates definitively that RIXS is not confined to 2D materials such as cuprates and can be a useful tool for the study of magnetic interaction in a wide class of 3$d$ transition metal systems.

High-resolution resonant inelastic X-ray scattering with soft X-rays at the ADRESS beamline of the Swiss light source: Instrumental developments and scientific highlights

The experimental development of the resonant inelastic X-ray scattering (RIXS) technique in the soft X-ray energy range has been tremendous during the last years. The ADRESS beamline at the Paul Scherrer Institut in Switzerland and its RIXS spectrometer SAXES has boosted the scientific capabilities with soft X-ray RIXS. Increased resolving power above 10,000 and the possibility to rotate the spectrometer to different scattering geometries allows analyzing the collective behavior of charge, orbital and spin excitations by assessing their momentum dependence. Focus of most projects at this facility lies in the investigation of low- and medium-energy excitations in correlated electron materials. In addition ADRESS has also been used for RIXS investigations on molecules in the liquid and gaseous phase. This review reports on the recent extension of the optics of the SAXES RIXS spectrometer with an additional grating optimized for the spectral range from ca. 400 to 700eV. Furthermore, the scientific opportunities emerging from ADRESS are highlighted in RIXS studies on quasi one-dimensional cuprates, oxide heterostructures and a weakly correlated broad band material.

Resonant Inelastic X-ray Scattering at the ESRF: Hard and Soft X-rays

The technique of Resonant Inelastic X-ray Scattering (RIXS) has been exploited at the ESRF since the very early days of the facility in the 1990s. Of particular importance has been the pioneering hard X-ray work on ID16 and that by the Milano group of L. Braicovich and G. Ghiringhelli in collaboration with the ESRF at the soft X-ray beamline (originally on ID12B and then at ID08). The success of these activities has in many cases led to the development of the technique at other facilities. Both the hard and soft X-ray RIXS facilities at the ESRF will be upgraded in the next two years so it is timely to briefly outline what scientific problems can be addressed by the method, what the current status is at the ESRF, and how the experimental capabilities will be enhanced in the near future.