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.