Pressure-driven insulator-metal transition in cubic phase UO₂

¹ Science and Technology on Surface Physics and Chemistry Laboratory - P.O. Box 9-35, Mianyang 621908, China
² Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory Upton, NY 11973, USA
³ Department of Physics, University of Fribourg - 1700 Fribourg, Switzerland

Received: 28 September 2017
Accepted: 24 October 2017

Abstract

Understanding the electronic properties of actinide oxides under pressure poses a great challenge for experimental and theoretical studies. Here, we investigate the electronic structure of cubic phase uranium dioxide at different volumes using a combination of density functional theory and dynamical mean-field theory. The ab initio calculations predict an orbital-selective insulator-metal transition at a moderate pressure of ∼45 GPa. At this pressure the uranium's 5f_5/2 state becomes metallic, while the 5f_7/2 state remains insulating up to about 60 GPa. In the metallic state, we observe a rapid decrease of the 5f occupation and total angular momentum with pressure. Simultaneously, the so-called “Zhang-Rice state”, which is of predominantly 5f_5/2 character, quickly disappears after the transition into the metallic phase.