Theory of valence transitions in Ytterbium and Europium intermetallics

The exact solution of the multi-component Falicov-Kimball model in infinite-dimensions is presented and used to discuss a new fixed point of valence fluctuating intermetallics with Yb and Eu ions. In these compounds, temperature, external magnetic field, pressure, or chemical pressure induce a transition between a metallic state with the f-ions in a mixed-valent (non-magnetic) configuration and a semi-metallic state with the f-ions in an integral-valence (paramagnetic) configuration. The zero-field transition occurs at the temperature Tv, while the zero-temperature transition sets in at the critical field Hc. We present the thermodynamic and dynamic properties of the model for an arbitrary concentration of d- and f-electrons. For large U, we find a MI transition, triggered by the temperature or field-induced change in the f-occupancy.