No abstract

Earth's interior consists primarily of an insulating rocky mantle [1, 2] and a metallic iron-dominant core [3, 4]. Recent work has shown that mountainscale structures at the core-mantle boundary may be highly enriched in , reported to exhibit high conductivity and metallic behavior at extreme pressure-temperature (P-T ) conditions [9]. However, the underlying electronic processes in FeO remain poorly understood and controversial. Here we systematically explore the electronic structure of B1-FeO at extreme conditions with large-scale theoretical modeling using state-of-the-art embedded dynamical mean field theory (eDMFT) [10]. Fine sampling of the phase diagram at more than 350 volume-temperature conditions reveals that, instead of sharp metallization, compression of FeO at high temperatures induces a gradual orbitally selective insulator-metal transition. Specifically, at P-T conditions of the lower mantle, FeO exists in an intermediate "quantum critical" state, characteristic of strongly correlated electronic matter [5, 6, 11]. Transport in this regime, distinct from insulating or metallic behavior, is marked by incoherent diffusion of electrons in the conducting t 2g orbital and a band gap in the e g orbital, resulting in moderate electrical conductivity (∼ 10 5 S/m) with modest P-T dependence as observed in experiments [9]. FeO-rich regions in Earth's lowermost mantle could thus influence electromagnetic interactions between the mantle and the core, producing several features observed in Earth's rotation and magnetic field evolution [14].