Quantum spin Hall effect in rutile-based oxide multilayers

TL;DR

This paper demonstrates that rutile-based oxide multilayers exhibit quantum spin Hall states due to Dirac points that become gapped by spin-orbit coupling, leading to topologically nontrivial edge states.

Contribution

It reveals the topological properties of specific rutile multilayers and discusses how mirror-symmetry breaking can induce a transition to a strong topological insulator.

Findings

Presence of Dirac cones in multilayers with four Dirac points along Γ-M.

Spin-orbit coupling opens gaps, resulting in quantum spin Hall states.

Model Hamiltonian shows mirror-symmetry breaking can induce a topological phase transition.

Abstract

Dirac points in two-dimensional electronic structures are a source for topological electronic states due to the $\pm \pi$ Berry phase that they sustain. Here we show that two rutile multilayers (namely (WO$_2$)$_2$/(ZrO$_2$)$_n$ and (PtO$_2$)$_2$/(ZrO$_2$)$_n$, where an active bilayer is sandwiched by a thick enough (n=6 is sufficient) band insulating substrate, show semi-metallic Dirac dispersions with a total of four Dirac cones along the $\Gamma-M$ direction. These become gapped upon the introduction of spin-orbit coupling, giving rise to an insulating ground state comprising four edge states. We discuss the origin of the lack of topological protection in terms of the valley spin-Chern numbers and the multiplicity of Dirac points. We show with a model Hamiltonian that mirror-symmetry breaking would be capable of creating a quantum phase transition to a strong topological insulator, with a single Kramers pair per edge.