# Exploring itinerant states in divalent hexaborides using rare-earth $L$ edge resonant inelastic X-ray scattering

## TL;DR

This study uses rare-earth $L$-edge RIXS to investigate the electronic states in divalent hexaborides, revealing distinct scattering processes and the potential of RIXS to probe itinerant $f$-electron states.

## Contribution

It demonstrates the application of $L$-edge RIXS to analyze the unoccupied states and scattering processes in divalent hexaborides, highlighting its utility in studying $f$-electron itinerant states.

## Key findings

- RIXS features at two distinct resonances with angle dependence.
- Spectra resemble unoccupied 5$d$ density of states from DFT calculations.
- Anomalous scattering observed at higher incident energies without absorption features.

## Abstract

We present a study of resonant inelastic X-ray scattering (RIXS) spectra collected at the rare-earth $L$ edges of divalent hexaborides YbB$_6$ and EuB$_6$. In both systems, RIXS-active features are observed at two distinct resonances separated by $\sim10$ eV in incident energy, with angle-dependence suggestive of distinct photon scattering processes. RIXS spectra collected at the divalent absorption peak strongly resemble the unoccupied 5$d$ density of states calculated using density functional theory, an occurrence we ascribe to transitions between weakly-dispersing 4$f$ and strongly dispersing 5$d$ states. In addition, anomalous resonant scattering is observed at higher incident energy, where no corresponding absorption feature is present. Our results suggest the far-reaching utility of $L$-edge RIXS in determining the itinerant-state properties of $f$-electron materials.