Comparison of bulk-sensitive spectroscopic probes of Yb valence in Kondo systems

We exploited complementary synchrotron radiation spectroscopies to study the Yb 4f electronic configuration in three representative intermediate-valence materials: YbAl3, YbInCu4, and YbCu2Si2. High-resolution x-ray absorption PFY-XAS, resonant inelastic x-ray scattering RIXS, and hard-x-ray photoemission HAXPES data all show characteristic temperature-dependent changes of the Yb valence. For each material, the increments measured from low 20 K to high 300 K temperature by the different probes are quite similar. The estimated RIXS and XAS valences are consistently higher than the HAXPES values. We briefly discuss the possible origin of this discrepancy.