Theory of valence transitions in ytterbium-based compounds
  The anomalous behavior of YbInCu4 and similar compounds is modeled by the exact solution of the spin one-half Falicov-Kimball model in infinite dimensions. The valence-fluctuating transition is related to a metal-insulator transition caused by the Falicov-Kimball interaction, and triggered by the change in the f-occupancy. 
V. Zlatic' (Institute of Physics, Zagreb and Newton Institute,   Cambridge) and J.K. Freericks (Department of Physics, Georg...