| The possibility of describing the spectral properties of intermediate valence compounds (IVC), like many Ce- and Yb-based intermetallics, by the simple Anderson Impurity Model (AIM), has spurred a heated debate in the literature. Traditional photoemission experiments, which are very surface sensitive, give conflicting results. On the other hand, recent soft x-ray experiments have shown that the surface and bulk electronic properties of these materials may be quite different. The bulk sensitivity of the spectroscopic probes may be further increased using higher energy photons, in the hard x-ray range. We have performed a series of hard x-ray experiments on three representative Yb IVCs: YbAl3, YbInCu4 and YbCu2Si2. Complementary hard x-ray photoemission (HAXPES), resonant inelastic x-ray scattering (RIXS) and high-resolution x-ray absorption (PFY-XAS) data, provided us with independent, bulk-sensitive spectroscopic estimates of the Yb valence in the various materials. While HAXPES allows to overcome the surface sensitivity of low-energy photoemission data and to access more directly the Yb 4f states, XAS and RIXS still prove to be less sensitive to the surface disorder and therefore are a more reliable probe of the bulk electronic configuration. These results confirm at a semi-quantitative level the crucial (T/TK) scaling predicted by the AIM. |
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