Pressure-Induced Site-Selective Mott Insulator-Metal Transition inFe2O3

Abstract

We provide experimental and theoretical evidence for a pressure-induced Mott insulator-metal transition in Fe2O3 characterized by site-selective delocalization of the electrons. Density functional plus dynamical mean-field theory (DFT+DMFT) calculations, along with Mössbauer spectroscopy, x-ray diffraction, and electrical transport measurements on Fe2O3 up to 100 GPa, reveal this site-selective Mott transition between 50 and 68 GPa, such that the metallization can be described by (Fe3+HSVI)2O3 [R3¯c structure]→50 GPa(Fe3+HSVIII FeVIM)O3 [P21/n structure]→68 GPa(FeMVI)2O3[Aba2/PPv structure]. Within the P21/n crystal structure, characterized by two distinct coordination sites (VI and VIII), we observe equal abundances of ferric ions (Fe3+) and ions having delocalized electrons (FeM), and only at higher pressures is a fully metallic high-pressure structure obtained, all at room temperature. 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. Above approximately 50 GPa, Fe2O3 is a strongly correlated metal with reduced electron mobility (large band renormalizations) of m*/m∼4 and 6 near the Fermi level. Importantly, upon decompression, we observe a site-selective (metallic) to conventional Mott insulator phase transition (Fe3+HSVIII FeVIM)O3→50 GPa(Fe3+HSVIII FeVI3+HS)O3 within the same P21/n structure, indicating a decoupling of the electronic and lattice degrees of freedom. Our results offer a model for understanding insulator-metal transitions in correlated electron materials, showing that the interplay of electronic correlations and crystal structure may result in rather complex behavior of the electronic and magnetic states of such compounds.3 MoreReceived 15 December 2017Revised 1 June 2018DOI:https://doi.org/10.1103/PhysRevX.8.031059Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBand gapDensity of statesElectrical conductivityInsulatorsMagnetic phase transitionsMetal-insulator transitionMetalsPhase transitionsPressure effectsSolid-solid transformationsPhysical SystemsCrystal structuresMott insulatorsPolycrystalline materialsStrongly correlated systemsTechniquesBand structure methodsCryogenicsDensity functional theoryDynamical mean field theoryLiquid helium coolingLiquid nitrogen coolingMössbauer spectroscopyTransport techniquesX-ray diffractionX-ray powder diffractionCondensed Matter, Materials & Applied Physics