Dirac topological insulator in the d$_{z^2}$ manifold of a honeycomb oxide

TL;DR

This paper demonstrates that a honeycomb oxide system with dominant d$_{z^2}$ orbitals can host topologically non-trivial states, with a SOC-induced gap, offering a new platform for oxide-based topological insulators.

Contribution

It introduces a general recipe for realizing topological insulators in oxide systems based on a single orbital near the Fermi level, specifically using d$_{z^2}$ orbitals in honeycomb lattices.

Findings

Topologically non-trivial states can be achieved in honeycomb oxides with dominant d$_{z^2}$ orbitals.

The SOC-induced gap scales linearly with SOC strength.

The system exhibits quantum Hall effects similar to graphene, but in a d-electron context.

Abstract

We show by means of ab initio calculations and tight-binding modeling that an oxide system based on a honeycomb lattice can sustain topologically non-trivial states if a single orbital dominates the spectrum close to the Fermi level. In such situation, the low energy spectra is described by two Dirac equations that become non-trivially gapped when spin-orbit coupling (SOC) is switched on. We provide one specific example for this but the recipe is general. We discuss a realization of this starting from a conventional spin-a-half honeycomb antiferromagnet whose states close to the Fermi energy are d$_{z^2}$ orbitals. Switching off magnetism by atomic substitution and ensuring that the electronic structure becomes two-dimensional is sufficient for topologicality to arise in such a system. We show that the gap in such model scales linearly with SOC, opposed to other oxide-based topological insulators, where smaller gaps tend to appear by construction of the lattice. We also provide a study of the quantum Hall effect in such system, showing the close connections with the physics of graphene but in a d-electron system.