Topological phases in layered pyrochlore oxide thin films along the [111] direction

TL;DR

This paper theoretically investigates layered pyrochlore oxide thin films along the [111] direction, identifying conditions for topological insulator and Chern insulator phases driven by spin-orbit coupling and electron interactions.

Contribution

It introduces a multi-band Hubbard model for pyrochlore thin films and predicts topological phases in specific geometries, highlighting potential materials and interaction effects.

Findings

Identification of Z2 topological phases in certain geometries.

Prediction of Chern insulator phases at half-filling.

Bilayer and trilayer structures support robust topological states.

Abstract

We theoretically study a multi-band Hubbard model of pyrochlore oxides of the form A$_2$B$_2$O$_7$, where B is a heavy transition metal ion with strong spin-orbit coupling, in a thin film geometry orientated along the [111] direction. Along this direction, the pyrochlore lattice consists of alternating kagome and triangular lattice planes of B ions. We consider a single kagome layer, a bilayer, and the two different trilayers. As a function of the strength of the spin-orbit coupling, the direct and indirect $d$-orbital hopping, and the band filling, we identify a number of scenarios where a non-interacting time-reversal invariant Z$_2$ topological phase is expected and we suggest some candidate materials. We study the interactions in the half-filled $d$-shell within Hatree-Fock theory and identify parameter regimes where a zero magnetic field Chern insulator with Chern number $\pm1$ can be found. The most promising geometries for topological phases appear to be the bilayer which supports both a Z$_2$ topological insulator and a Chern insulator, and the triangular-kagome-triangular trilayer which supports a relatively robust Chern insulator phase.