Valence Transitions in Yb1+xIn1-xCu4 Studied by High-resolution X-ray Absorption Spectroscopy, X-ray Diffraction, and Photoelectron Spectroscopy

Temperature- and pressure-induced valence transitions in the Yb-rich compounds Yb1+xIn1-xCu4 were studied directly by the high-resolution x-ray absorption spectroscopy. We observed a correlation between the temperature dependence of chi T and the Yb valence which could be described by the Anderson model, where chi and T are magnetic susceptibility and temperature, respectively. The valence transition temperature of Yb1+xIn1-xCu4 was found to be insensitive to the chemical pressure compared to to the case of YbIn1-xAgxCu4. This difference could be attributed to the difference in the electronic structure above the Fermi level. The shift of T-upsilon to higher temperatures with increasing x in Yb1+xIn1-xCu4 is interpreted to be caused by the stronger hybridization contributed by the additional Yb site at the In site. Hydrostatic pressure dependence of the Yb valence in Yb1.06In0.94Cu4 showed an anomaly. The Yb valence decreased at the pressure range of 5-20 GPa where an anomaly was also observed in the pressure dependence of the lattice constant.