An x-ray spectroscopy study was performed for YbCu5-xAl x (x = 0.0-2.0) using high-resolution partial-fluorescence yield (PFY) and resonant inelastic x-ray scattering (RIXS) at the Yb L3 absorption edge. From a careful analysis of the PFY and RIXS spectra, the mean-valence of Yb was estimated and is found to increase quite rapidly for compositions between 0 ≤ x ≤ 1.0, indicating strong intermediate-valence behavior. The mean valence continues to increase gradually with x and becomes nearly trivalent for x = 2.0. Our results, however, reveal that valence fluctuation occurs even at x = 1.5, for which non-Fermi liquid quantum critical behavior is known. The valence evolution cannot be explained solely in terms of chemical pressure effects. The study suggests the role of valence-coupled spin fluctuations for the quantum critical behavior.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)