Photoemission study of valence fluctuation inYbCu2

Abstract
Mixed-valence YbCu2 has been studied by x-ray and ultraviolet photoemission spectroscopy (XPS and UPS). UPS results reveal a bulk divalent (4f14→4f13) peak ∼0.3 eV below the Fermi level, and a valence of 2.2 is deduced from XPS. These values are compared with the ground-state magnetic susceptibility, the specific heat, and the magnetic relaxation rate of 4f electrons by using the results of the degenerate impurity Anderson model. The 4f–5d–conduction-band hybridization is suggested to be more important than the 4f–sp–conduction-band hybridization.