Emergent topological states via digital (001) oxide superlattices

Oxide heterostructures exhibit many intriguing properties. Here we provide design principles for inducing multiple topological states in (001) (AMO₃)₁/(AM’O₃)₁ oxide superlattices. Aided by first-principles calculations and model analysis, we show that a (SrMO₃)₁/(SrM’O₃)₁ superlattice (M = Nb, Ta and M’ = Rh, Ir) is a strong topological insulator with Z₂ index (1;001). More remarkably, a (SrMoO₃)₁/(SrIrO₃)₁ superlattice exhibits multiple coexisting topological insulator (TI) and topological Dirac semi-metal (TDS) states. The TDS state has a pair of type-II Dirac points near the Fermi level and symmetry-protected Dirac node lines. The surface TDS Dirac cone is sandwiched by two surface TI Dirac cones in the energy-momentum space. The non-trivial topological properties arise from the band inversion between d orbitals of two dissimilar transition metal atoms and a particular parity property of (001) superlattice geometry. Our work demonstrates how to induce non-trivial topological states in (001) perovskite oxide heterostructures by rational design.