Dimensionality-Controlled Insulator-Metal Transition and Correlated Metallic State in 5d Transition Metal Oxides Srn+1IrnO3n+1 (n=1, 2, and ∞)

Abstract

We investigated the electronic structures of the $5d$ Ruddlesden-Popper series ${\mathrm{Sr}}_{n+1}{\mathrm{Ir}}_n{\mathrm{O}}_{3n+1}$ ($n=1$, 2, and $\infty$) using optical spectroscopy and first-principles calculations. As $5d$ orbitals are spatially more extended than $3d$ or $4d$ orbitals, it has been widely accepted that correlation effects are minimal in $5d$ compounds. However, we observed a Mott insulator-metal transition with a change of bandwidth as we increased $n$. In addition, the artificially synthesized perovskite ${\mathrm{SrIrO}}_3$ showed a very large mass enhancement of about 6, indicating that it was in a correlated metallic state.