Interaction-driven spin-orbit effects and Chern insulating phases in corundum-based $4d$ and $5d$ oxide honeycomb lattices

TL;DR

This study uses density functional theory to identify and analyze topologically nontrivial phases, including quantum anomalous Hall insulators, in corundum-based 4d and 5d oxide honeycomb lattices, revealing the influence of spin-orbit coupling and electronic correlations.

Contribution

It demonstrates the emergence of Chern insulating phases in corundum-based oxide honeycomb lattices and explores the effects of Coulomb interactions and spin-orbit coupling on their topological properties.

Findings

Tc and Pt layers exhibit Chern insulating phases with gaps of 54 and 59 meV.

The Chern phase in Tc is sensitive to Coulomb repulsion, transitioning to a trivial metal beyond Uc=2.5 eV.

Os layer is a FM Mott insulator with a high orbital moment induced by SOC.

Abstract

Using density functional theory calculations with a Hubbard $U$, we explore topologically nontrivial phases in $X_2$O$_3$ honeycomb layers with $X=$ $4d$ and $5d$ cation inserted in the band insulator $\alpha$-Al$_2$O$_3$ along the [0001]-direction. Several promising candidates for quantum anomalous Hall insulators (QAHI) are identified. In particular, for $X$=Tc and Pt spin-orbit coupling (SOC) opens a gap of 54 and 59 meV, respectively, leading to Chern insulators (CI) with $C$=--2 and --1. The nature of different Chern numbers is related to the corresponding spin textures. The Chern insulating phase is sensitive to the Coulomb repulsion strength: $X$=Tc undergoes a transition from a CI to a trivial metallic state beyond a critical strength of $U_c$ =2.5 eV. A comparison between the isoelectronic metastable FM phases of $X$=Pd and Pt emphasizes the intricate balance between electronic correlations and SOC: while the former is a trivial insulator, the latter is a Chern insulator. In addition, $X$=Os turns out to be a FM Mott insulator with an unpaired electron in the $t_{2g}$ manifold where SOC induces an unusually high orbital moment of 0.34 $\mu_{\rm B}$ along the $z$-axis. Parallels to the $3d$ honeycomb corundum cases are discussed.