Nature of the Insulating Ground State of the 5d PostPerovskite CaIrO3

TL;DR

This study uses density functional theory to show that CaIrO3's insulating state is a spin-orbit Slater insulator, driven by antiferromagnetic order and spin-orbit coupling, revealing a complex interplay of electronic and magnetic properties.

Contribution

It demonstrates that CaIrO3's insulating ground state arises from a combined effect of antiferromagnetic order and spin-orbit coupling, classifying it as a spin-orbit Slater insulator.

Findings

CaIrO3 exhibits large t2g state splittings and one-dimensional electronic states.

Hybrid DFT captures the antiferromagnetic order and insulating gap.

DFT + DMFT confirms the metal-insulator and magnetic phase transition.

Abstract

The insulating ground state of the 5d transition metal oxide CaIrO3 has been classified as a Mott-type insulator. Based on a systematic density functional theory (DFT) study with local, semilocal, and hybrid exchange-correlation functionals, we reveal that the Ir t2g states exhibit large splittings and one-dimensional electronic states along the c axis due to a tetragonal crystal field. Our hybrid DFT calculation adequately describes the antiferromagnetic (AFM) order along the c direction via a superexchange interaction between Ir4+ spins. Furthermore, the spin-orbit coupling (SOC) hybridizes the t2g states to open an insulating gap. These results indicate that CaIrO3 can be represented as a spin-orbit Slater insulator, driven by the interplay between a long-range AFM order and the SOC. Such a Slater mechanism for the gap formation is also demonstrated by the DFT + dynamical mean field theory calculation, where the metal-insulator transition and the paramagnetic to AFM phase transition are concomitant with each other.