Chern and Z topological insulating phases in perovskite-derived 4d and 5d oxide buckled honeycomb lattices.

Based on density functional theory calculations including a Coulomb repulsion parameter U, we explore the topological properties of (LaXO)/(LaAlO) (111) with X = 4d and 5d cations. The metastable ferromagnetic phases of LaTcO and LaPtO with preserved P321 symmetry 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, 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 to a. 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 (XO)/(AlO) (0001) honeycomb corundum layers are discussed. Additionally, non-magnetic systems with X = Mo and W are identified as potential candidates for Z topological insulators at a with band gaps of 26 and 60 meV, respectively. The computed edge states and Z invariants underpin the non-trivial topological properties.