Emergent topological states via digital (001) oxide superlattices

TL;DR

This paper demonstrates how to engineer multiple topological states, including strong topological insulators and Dirac semi-metals, in (001) oxide superlattices through first-principles calculations and design principles.

Contribution

It provides a systematic design approach for inducing topological states in (001) oxide superlattices, revealing new topological phases in specific material combinations.

Findings

(Sr$M$O$_3$)$_1$/(Sr$M'$O$_3$)$_1$ is a strong topological insulator.

(SrMoO$_3$)$_1$/(SrIrO$_3$)$_1$ exhibits coexisting TI and TDS states.

The topological properties originate from band inversion and superlattice symmetry.

Abstract

Oxide heterostructures exhibit many intriguing properties. Here we provide design principles for inducing multiple topological states in (001) ($AM$O$_3$)$_1$/($AM'$O$_3$)$_1$ oxide superlattices. Aided by first-principles calculations and model analysis, we show that a (Sr$M$O3)$_1$/(Sr$M'$O$_3$)$_1$ superlattice ($M$ = Nb, Ta and $M'$ = Rh, Ir) is a strong topological insulator with $Z_2$ 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 nontrivial topological states in (001) perovskite oxide heterostructures by rational design.