Bandwidth-Controlled Insulator-Metal Transition and Correlated Metallic State in 5$d$ Transition Metal Oxides Sr$_{n+1}$Ir$_{n}$O$_{3n+1}$ ($n$=1, 2, and $\infty$)

TL;DR

This study explores how increasing bandwidth in 5d iridates induces an insulator-to-metal transition, revealing significant electron correlation effects even in extended orbitals, with implications for understanding correlated metallic states.

Contribution

It demonstrates a bandwidth-controlled insulator-metal transition in Sr$_{n+1}$Ir$_{n}$O$_{3n+1}$ series and uncovers strong correlation effects in SrIrO$_{3}$.

Findings

Bandwidth increase induces insulator-metal transition.

SrIrO$_{3}$ exhibits a large mass enhancement (~6).

Correlation effects are significant despite extended 5d orbitals.

Abstract

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