We clarify the origin of the strikingly different spectroscopic properties of the chemically similar compounds ${\mathrm{NaOsO}}_3$ and ${\mathrm{LiOsO}}_3$. Our first-principle, many-body analysis demonstrates that the highly sensitive physics of these two materials is controlled by their proximity to an adjacent Hund’s-Mott insulating phase. Although $5d$ oxides are mildly correlated, we show that the cooperative action of intraorbital repulsion and Hund’s exchange becomes the dominant physical mechanism in these materials if their $t_{2g}$ shell is half filled. Small material specific details hence result in an extremely sharp change of the electronic mobility, explaining the surprisingly different properties of the paramagnetic high-temperature phases of the two compounds.

• Received 15 October 2019
• Revised 10 May 2020
• Accepted 25 August 2020

DOI:https://doi.org/10.1103/PhysRevLett.125.166402