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

摘要

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