Semimetal and Topological Insulator in Perovskite Iridates

TL;DR

This paper investigates the electronic phases of perovskite iridates, revealing how structural and spin-orbit effects lead to metallic, topological insulator, and band insulator states, and proposes new candidate materials.

Contribution

It constructs a tight-binding model for SrIrO3, explaining its metallic state and topological phase transitions, and suggests new layered iridate compounds as topological insulators.

Findings

SrIrO3 has a line node in its band structure that suppresses magnetic ordering.

Introducing a staggered potential induces a transition from a line node to nodal points and then to topological insulator phases.

Materials like Sr2IrRhO6 are potential strong topological insulators.

Abstract

The two-dimensional layered perovskite Sr2IrO4 was proposed to be a spin-orbit Mott insulator, where the effect of Hubbard interaction is amplified on a narrow J_{eff} = 1/2 band due to strong spin-orbit coupling. On the other hand, the three-dimensional orthorhombic perovskite (Pbnm) SrIrO3 remains metallic. To understand the physical origin of the metallic state and possible transitions to insulating phases, we construct a tight-binding model for SrIrO3. The band structure possesses a line node made of J_{eff} = 1/2 bands below the Fermi level. As a consequence, instability towards magnetic ordering is suppressed and the system remains metallic. This line node, originating from the underlying crystal structure, turns into a pair of three-dimensional nodal points on the introduction of a staggered potential or spin-orbit coupling strength between alternating layers. Increasing this potential beyond a critical strength induces a transition to a strong topological insulator, followed by another transition to a normal band insulator. We propose that materials constructed with alternating Ir- and Rh-oxide layers along the (001) direction, such as Sr2IrRhO6, are candidates for a strong topological insulator.