Quantum spin Hall effect in rutile-based oxide multilayers

Dirac points in two-dimensional electronic structures are a source for topological electronic states due to the ±? Berry phase that they sustain. Here we show that two rutile multilayers [namely (WO2)2/(ZrO2)n and (PtO2)2/(ZrO2)n], where an active bilayer is sandwiched by a thick enough (n=6 is sufficient) band insulating substrate, show semimetallic Dirac dispersions with a total of four Dirac cones along the ?-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.