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Resonant inelastic x-ray scattering at the actinide M4,5-edges

Martin Sundermann1,2, Henrik Hahn3, Denise S. Christovam1, Maurits W. Haverkort3, Roberto Caciuffo4,5, Bernhard Keimer6, Liu Hao Tjeng1, Andrea Severing1,7, and Hlynur Gretarsson2,6

  • Present address: Max Planck Institute for Solid State Research, Heisenbergstraße 1, 70569 Stuttgart, Germany.
  • Contact author: andrea.severing@cpfs.mpg.de
  • Contact author: hlynur.gretarsson@desy.de
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Phys. Rev. Research 7, 043081 – Published 21 October, 2025

DOI: https://doi.org/10.1103/twsv-xh5j

Abstract

Understanding the electronic structure of actinide materials is crucial for both fundamental research and nuclear applications. The partially filled 5f shells exhibit complex behavior due to strong correlations and ligand hybridization, requiring advanced spectroscopic techniques. Here, we report on the development and application of high-resolution valence band resonant inelastic x-ray spectroscopy (VB-RIXS) experiments at the uranium M4,5 edges (3551 and 3725 eV). We present data of UO2, a well-established model actinide compound. VB-RIXS is particularly well suited for probing the 5f-shell electronic structure, as it probes, in contrast to core-to-core RIXS, excitations without leaving a high-energy core hole in the final state. In VB-RIXS, we achieve energy resolutions of 50 meV (M5) and 90 meV (M4), enabling the resolution of multiplet excitations and crystal-field effects, as well as charge-transfer and fluorescencelike features with unprecedented clarity. As such, high-resolution VB-RIXS offers direct insights into both low-energy, near-ground-state properties and high-energy hybridization and covalency effects. Our results demonstrate the power of VB-RIXS as a versatile and powerful tool for probing the strongly correlated electronic structure of actinide materials, providing essential input for quantitative modeling and the validation of theoretical concepts.

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Phys. Rev. Research 7, 043081– Published 21 October, 2025
  • Received 30 July 2025
  • Accepted 19 September 2025
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