Site-selective Mott insulator-metal transition in Fe₂O₃ under ultra-high pressures

The insulator-metal transition, induced by pressure, composition or by other means, represents perhaps the most profound transformation of the chemical bond in materials. Combining density functional plus dynamical mean-field theory (DFT+DMFT) calculations with experiment, we demonstrate that upon compression of Fe₂O₃ a novel type of Mott insulator-metal transition occurs, which is characterized by site-selective delocalization of the electrons [1]. Within the P2₁/n crystal structure, which is stable in the pressure range 45-68 GPa, we observe equal abundances of ferric ions (Fe³⁺) and ions having delocalized electrons (Fe^M). Thereby the transition is characterized by delocalization/metallization of the 3d electrons on half the Fe sites, with a site-dependent collapse of local moments. Upon further compression above 75 GPa, we predict another phase transition, to a metal with a post-perovskite crystal structure and site-selective local moments [2]. Our results suggest that site-selective local moments in Fe₂O₃ persist up to ultra-high pressure of ~200-250 GPa, i.e. to pressure sufficiently above that at the core-mantle boundary.

[1] E. Greenberg, et al., Phys. Rev. X 8, 031059 (2018).
[2] I. Leonov, G. Kh. Rozenberg, I. A. Abrikosov (submitted)