Geotherm tracks the quantum critical regime of FeO: an eDMFT study

A potentially key contributor to compositions and processes at Earth’s core-mantle boundary, FeO has demonstrated over the past several decades an astonishing variety of conductive, magnetic, and structural phases, depending on local pressure (P) and temperature (T) conditions. What presently remains to be well understood is the physical picture underlying this unconventional behavior and its geophysical implications. Here, we seek to rectify this deficiency by analyzing (B1-type) FeO’s electronic structure across its (P,T) phase diagram, through large scale theoretical modeling, using state-of-the-art “embedded dynamical mean-field theory” (eDMFT). We establish that FeO’s phase diagram comprises 3 distinct regions, which emerge around the Mott point and possess unique transport trends. Of these, we find that (P,T) conditions which are largely relevant for FeO in geophysics occupy precisely the intermediate quantum critical regime, a wide finite-temperature region separating the metallic and the insulating phases of matter. Quantum critical transport found here displays weak P/T dependence and moderate electrical resistance around the Mott-Ioffe-Regel limit, which is dominated by strong electron-electron scattering.