Abstract
We have investigated the electronic structure of the high oxidation state material within the framework of the Zaanen-Sawatzky-Allen phase diagram. While -based compounds such as and can be classified as small-gap or metallic negative-charge-transfer systems, we find using photoelectron spectroscopy that is a robust insulator despite the fact that its Cr ions have an even higher formal valence state of 5+. We reveal using band-structure calculations that the tetrahedral coordination of the ions in plays a decisive role, namely to diminish the bonding of the Cr states with the top of the O valence band. This finding not only explains why the charge-transfer energy remains effectively positive and the material stable, but also opens up a new route to create doped carriers with symmetries different from those of other transition-metal ions.
- Received 25 October 2013
- Revised 19 July 2014
DOI:https://doi.org/10.1103/PhysRevB.90.085106
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