Pressure-volume relationship,quasiparticle density of states and hybridization gap of mixed valence EuO

Thes-f model, extended by a hybridization term, is used to investigate the pressure-dependence of the quasiparticle density of states of paramagnetic EuO (T=300K). We find a semiconductor-metal transition of first order atp _c =301 kbar, which manifests itself by a striking discontinuity in the pressure-volume relationship, in almost exact agreement with the experiment 5]. The transition is due to the valence-change Eu²⁺Eu³⁺ of the Europium ion.-Special attention is devoted to the competing influence of thes-f exchange interaction and thes-f hybridization between extendeds-band states and localizedf-levels on characteristic details of the phase transition. Exchange and hybridization are therefore taken into account exactly, while the electron hopping is treated in an approximate many body theory.-As a typical feature we find a small hybridization gap in the quasiparticle density of states. Forp<p _c the chemical potential lies always within this gap, so that the material is a narrow gap semiconductor. Forp<p _c the gap does survive, but then is below the gap allowing metallic conductivity.