Abstract
We study pressure-induced isostructural electronic phase transitions in the prototypical mixed valence and strongly correlated material EuO using the global-hybrid density functional theory. The simultaneous presence in the valence of highly localized - and -type bands and itinerant - and -type states, as well as the half-filled -type orbital shell with seven unpaired electrons on each Eu atom, have made the description of the electronic features of this system a challenge. The electronic band structure, density of states, and atomic oxidation states of EuO are analyzed in the 0–50 GPa pressure range. An insulator-to-metal transition at about 12 GPa of pressure was identified. The second isostructural transition at approximately 30–35 GPa, previously believed to be driven by an oxidation from Eu(II) to Eu(III), is shown instead to be associated with a change in the occupation of the Eu orbitals, as can be determined from the analysis of the corresponding atomic orbital populations. The Eu band is confined by the surrounding oxygens and split by the crystal field, which results in orbitals of symmetry (i.e., and , pointing along the Eu-O direction) being abruptly depopulated at the transition as a means to alleviate electron-electron repulsion in the highly compressed structures.
- Received 5 January 2021
- Revised 1 March 2021
- Accepted 22 April 2021
DOI:https://doi.org/10.1103/PhysRevLett.126.196404
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