Abstract
The I21 beamline at Diamond Light Source is dedicated to advanced resonant inelastic X-ray scattering (RIXS) for probing charge, orbital, spin and lattice excitations in materials across condensed matter physics, applied sciences and chemistry. Both the beamline and the RIXS spectrometer employ divergent variable-line-spacing gratings covering a broad energy range of 280-3000 eV. A combined energy resolution of ∼35 meV (16 meV) is readily achieved at 930 eV (530 eV) owing to the optimized optics and the mechanics. Considerable efforts have been paid to the design of the entire beamline, particularly the implementation of the collection mirrors, to maximize the X-ray photon throughput. The continuous rotation of the spectrometer over 150° under ultra high vacuum and a cryogenic manipulator with six degrees of freedom allow accurate mappings of low-energy excitations from solid state materials in momentum space. Most importantly, the facility features a unique combination of the high energy resolution and the high photon throughput vital for advanced RIXS applications. Together with its stability and user friendliness, I21 has become one of the most sought after RIXS beamlines in the world.
Highlights
Resonant inelastic X-ray scattering (RIXS) is a powerful spectroscopic technique capable of probing charge-neutral excitations, such as charge-transfer excitations, and orbital excitations, in a broad range of materials
We highlight that achieving the optimized energy resolution is straightforward owing to a free parameter available in the parameter set of the spectrometer
A similar situation happens for the spectrometer: the energy resolution deteriorates if the vertical acceptance of the spherical VLS (SVLS) grating is greater than 3 mrad, potentially due to nonnegligible coma and spherical aberrations
Summary
Resonant inelastic X-ray scattering (RIXS) is a powerful spectroscopic technique capable of probing charge-neutral excitations, such as charge-transfer excitations (e.g. between the ligand anions and the metal cations), and orbital excitations (e.g. dd or ff ), in a broad range of materials. With an improved energy resolution corresponding to the mid-infrared energy regime (i.e. 100–500 meV), RIXS, in particular the direct RIXS at the L-edges of transition metal elements, has shown to be capable of characterizing collective magnetic excitations in quantum magnetic materials (Braicovich et al, 2009; Ament et al, 2011). This newly revealed capability has excited considerable interest in the condensed matter physics community due to its complementarity with inelastic neutron scattering and because it is advantageous for probing magnetic excitations in small samples or complex systems with multiple magnetic elements.
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