# Chern and $Z_{2}$ topological insulating phases in perovskite-derived $4d$ and $5d$ oxide buckled honeycomb lattices

## TL;DR

This study uses density functional theory to identify and analyze topological insulating phases in perovskite-derived honeycomb lattices with 4d and 5d transition metals, revealing Chern insulators and Z2 topological insulators with significant band gaps.

## Contribution

It demonstrates the emergence of Chern and Z2 topological phases in specific oxide heterostructures, highlighting the role of strain, Hubbard U, and lattice parameters in stabilizing these phases.

## Key findings

- LaTcO3 and LaPtO3 exhibit Chern insulating phases with non-zero Chern numbers.
- Potential Z2 topological insulators identified among non-magnetic Mo and W compounds.
- Topological phases are sensitive to strain, Hubbard U, and lattice parameter variations.

## Abstract

Based on density functional theory calculations including a Coulomb repulsion parameter $U$, we explore the topological properties of (La$X$O$_3$)$_2$/(LaAlO$_3$)$_4$(111) with $X=$ $4d$ and $5d$ cations. The metastable ferromagnetic phases of LaTcO$_3$ and LaPtO$_3$ preserve P321 symmetry and emerge as Chern insulators (CI) with $C$=2 and 1 and band gaps of 41 and 38 meV at the lateral lattice constant of LaAlO$_3$, respectively. Berry curvatures, spin textures as well as edge states provide additional insight into the nature of the CI states. While for $X$=Tc the CI phase is further stabilized under tensile strain, for $X$=Pd and Pt a site disproportionation takes place when increasing the lateral lattice constant from $a_{\rm LAO}$ to $a_{\rm LNO}$. The CI phase of $X$=Pt shows a strong dependence on the Hubbard $U$ parameter with sign reversal for higher values associated with the change of band gap opening mechanism. Parallels to the previously studied ($X_2$O$_3$)$_1$/(Al$_2$O$_3$)$_5$(0001) honeycomb corundum layers are discussed. Additionally, non-magnetic systems with $X$=Mo and W are identified as potential candidates for $Z_2$ topological insulators at $a_{\rm LAO}$ with band gaps of 26 and 60 meV, respectively. The computed edge states and $Z_{2}$ invariants underpin the non-trivial topological properties.