We report on the most complete investigation to date of the -electron properties at the transition in elemental Ce by resonant inelastic x-ray scattering (RIXS). The Ce 2p3d-RIXS spectra were measured directly in the bulk material as a function of pressure through the transition. The spectra were simulated within the Anderson impurity model. The occupation number n(f) and f double occupancy were derived from the calculations in both gamma and alpha phases in the ground state. We find that the electronic structure changes result mainly from band formation of 4f electrons which concurs with reduced electron correlation and increased Kondo screening at high pressure.

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Resonant inelastic x-ray scattering spectra were measured for a series of Ce solid solutions (Ce-Th and Ce-Sc) across the gamma-alpha phase transition. They reveal a well-defined feature associated with the 4f2 configuration when the incident energy is tuned to the Ce L3 preedge region. This component is normally hidden in x-ray absorption spectra because of lifetime broadening. The f1/f2 ratio estimated by resonant inelastic x-ray scattering presents a sharp drop across the gamma-alpha transition and hysteresis as a function of temperature that closely resemble the magnetization loop. These measurements confirm recent dynamical mean-field theory calculations that unexpectedly predict significant double occupancy of f orbitals in the ground state.

A soft x-ray spectrometer based on the use of an elliptical focusing mirror and a plane varied line spacing grating is described. It achieves both high resolution and high overall efficiency while remaining relatively compact. The instrument is dedicated to resonant inelastic x-ray scattering studies. We set out how this optical arrangement was judged best able to guarantee performance for the 50 - 1000 eV range within achievable fabrication targets. The AERHA (adjustable energy resolution high acceptance) spectrometer operates with an effective angular acceptance between 100 and 250 μsr (energy dependent) and a resolving power well in excess of 5000 according to the Rayleigh criterion. The high angular acceptance is obtained by means of a collecting pre-mirror. Three scattering geometries are available to enable momentum dependent measurements with 135°, 90°, and 50° scattering angles. The instrument operates on the Synchrotron SOLEIL SEXTANTS beamline which serves as a high photon flux 2 × 200 μm(2) focal spot source with full polarization control.