Epitaxially stabilized iridium spinel oxide without cations in the tetrahedral site

TL;DR

This paper reports the fabrication of a novel iridium spinel oxide thin film, Ir2O4, which is an insulator with a unique crystal structure lacking A cations in the tetrahedral site, revealing new insights into iridium oxides.

Contribution

It introduces a new epitaxially stabilized iridium spinel oxide without tetrahedral A cations, expanding understanding of iridium oxide electronic states.

Findings

Ir2O4 is a narrow gap insulator.

Ir2O4 crystallizes in a spinel structure without A cations.

Strong spin-orbit coupling and Coulomb interactions likely cause the insulating state.

Abstract

Single-crystalline thin film of an iridium dioxide polymorph Ir2O4 has been fabricated by the pulsed laser deposition of LixIr2O4 precursor and the subsequent Li-deintercalation using soft chemistry. Ir2O4 crystallizes in a spinel (AB2O4) without A cations in the tetrahedral site, which is isostructural to lambda-MnO2. Ir ions form a pyrochlore sublattice, which is known to give rise to a strong geometrical frustration. This Ir spinel was found to be a narrow gap insulator, in remarkable contrast to the metallic ground state of rutile-type IrO2. We argue that an interplay of strong spin-orbit coupling and a Coulomb repulsion gives rise to an insulating ground state as in a layered perovskite Sr2IrO4.