Sr${}_3$Ir${}_2$O${}_7$F${}_2$: Topochemical conversion of a relativistic Mott state into a spin-orbit driven band insulator

Abstract

The topochemical transformation of single crystals of Sr${}_3$Ir${}_2$O${}_7$ into Sr${}_3$Ir${}_2$O${}_7$F${}_2$ is reported via fluorine insertion. Characterization of the newly formed Sr${}_3$Ir${}_2$O${}_7$F${}_2$ phase shows a nearly complete oxidation of Ir${}^{4+}$ cations into Ir${}^{5+}$ that in turn drives the system from an antiferromagnetic Mott insulator with a half-filled J${}_{eff}=1/2$ band into a nonmagnetic $J=0$ band insulator. First principles calculations reveal a remarkably flat insertion energy that locally drives the fluorination process to completion. Band structure calculations support the formation of a band insulator whose charge gap relies on the strong spin-orbit coupling inherent to the Ir metal ions of this compound.

10 pages, 7 figures