Observation of Kondo resonance inYbAl3

Anderson Hamiltonian parameters for mixed-valence ${\mathrm{YbAl}}_3$ were determined from the magnetic susceptibility, photoelectron-spectroscopy, and bremsstrahlung-isochromat-spectroscopy data. The 4$f^{13}$→4$f^{14}$ electron affinity energy is ∼0.5 eV and the hybridization between Yb 4f and Al conduction electrons is ∼0.05 eV, both of which are larger than conventional estimates. This hybridization and the resulting Kondo resonance are considered to play important roles for the anomalous properties of valence-fluctuating Yb compounds, as in the case of Ce compounds.