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

Abstract

Using density functional theory calculations with a Hubbard U, we explore topologically nontrivial phases in X2O3 honeycomb layers with X=4d and 5d cation inserted in the band insulator α-Al2O3 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 Uc=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 t2g manifold where SOC induces an unusually high orbital moment of 0.34 μB along the z-axis. Parallels to the 3d honeycomb corundum cases are discussed.