Kondo interactions from band reconstruction in YbInCu

Jarrige, I.*; Kotani, Akio*; Yamaoka, Hitoshi*; Tsujii, Naohito*; Ishii, Kenji; Upton, M.*; Casa, D.*; Kim, J. H.*; Gog, T.*; Hancock, J. N.*

We combine resonant inelastic X-ray scattering and model calculations in the Kondo lattice compound YbInCu, a system characterized by a dramatic increase in Kondo temperature and associated valence fluctuations below a first-order valence transition at T 42 K. The bulk-sensitive, element-specific, and valence-projected charge excitation spectra reveal an unusual quasigap in the Yb-derived state density which drives an instability of the electronic structure and renormalizes the low-energy effective Hamiltonian at the transition. Our results provide long-sought experimental evidence for a link between temperature-driven changes in the low-energy Kondo scale and the higher-energy electronic structure of this system.