Abstract
We provide experimental and theoretical evidence for a pressure-induced Mott insulator-metal transition in characterized by site-selective delocalization of the electrons. Density functional plus dynamical mean-field theory () calculations, along with Mössbauer spectroscopy, x-ray diffraction, and electrical transport measurements on up to 100 GPa, reveal this site-selective Mott transition between 50 and 68 GPa, such that the metallization can be described by . Within the crystal structure, characterized by two distinct coordination sites (VI and VIII), we observe equal abundances of ferric ions () and ions having delocalized electrons (), 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 electrons on half the Fe sites, with a site-dependent collapse of local moments. Above approximately 50 GPa, is a strongly correlated metal with reduced electron mobility (large band renormalizations) of and 6 near the Fermi level. Importantly, upon decompression, we observe a site-selective (metallic) to conventional Mott insulator phase transition within the same 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 More- Received 15 December 2017
- Revised 1 June 2018
DOI:https://doi.org/10.1103/PhysRevX.8.031059
Published 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 Society
Physics Subject Headings (PhySH)
Popular Summary
The distinction between insulator and metal is one of the most fundamental concepts of condensed-matter physics, having relevance to fields ranging from materials science to planetary physics. In particular, the Mott transition from insulator to metal, which is controlled by mutual interactions between electrons, plays a key role in transition-metal oxides. Here, we provide theoretical and experimental evidence for a complex pressure-induced insulator-to-metal transition in an archetypal “ Mott insulator” , whose insulating behavior is a result of strong on-site Coulomb repulsion of electrons.
This new transition is site selective—electrons in the orbital of the iron atoms are delocalized first at one location and then more generally throughout the crystal. Above a pressure of 50 GPa, the material forms a strongly correlated metal with reduced electron mobility compared to a normal metal. When the pressure is reduced, reverts to a conventional Mott insulator.
Our work highlights the interplay between electronic states and crystal structures and not only addresses a long-standing controversy regarding the high-pressure behavior of but also suggests that site-selective Mott transitions are important for transition-metal compounds in general.