Bulk sensitive spectroscopy for the valence transition in YbInCu4-based compounds

Bulk sensitive x-ray spectroscopy is performed to systematically study the effect of substitution on the valence transition in strongly correlated Yb compounds, such as Y0.1Yb0.9InCu4, YbInCu4, and YbIn0.88Ag0.12Cu4, and is compared with complementary magnetic-susceptibility results. High-resolution x-ray absorption spectroscopy with partial fluorescence yields mode and resonant x-ray emission spectroscopy is used to measure the valency change as a function of temperature. The valency change determined from spectroscopy exactly follows the temperature evolution of the magnetic susceptibility. The results confirm first-order transitions in Y0.1Yb0.9InCu4 and YbInCu4, while YbIn0.88Ag0.12Cu4 exhibits a continuous mixed-valence transition. The present results are in agreement with the mean-field Anderson lattice model theory of Goltsev and co-workers [Phys. Rev. B 63, 155109 (2001); J. Phys.: Condens. Matter 17, S813 (2005)], which includes the role of local deformations and Kondo volume collapse in the valence transition.