Abstract
While the theoretical and experimental study of topological phases of matter has experienced rapid growth over the last few years, there remain a relatively small number of material classes that have been experimentally shown to host these phases. Most of these materials contain bismuth, and none so far are oxides. In this work we make materials-specific predictions for topological phases using density functional theory combined with Hartree-Fock theory that includes the full orbital structure of the relevant iridium d-orbitals and the strong but finite spin-orbit coupling strength. We find Y2Ir2O7 bilayer and trilayer films grown along the [111] direction can support topological metallic phases with a direct gap of up to 0.05 eV, which could potentially bring transition metal oxides to the fore as a new class of topological materials with potential applications in oxide electronics.
Highlights
Topological phases have attracted much interest in recent years[1,2,3]
It is appreciated that three-dimensional pyrochlore iridates of the form R2Ir2O7, where R is a rare-earth element such as La, Y, or Eu may not have the correct electronic band structure features to support topological insulating states—namely that there is a (4-fold) band degeneracy at the Fermi energy protected by crystal symmetry[13,22,24]
We use first-principles density functional theory (DFT) calculations combined with Hartree-Fock theory to show that transition metal oxide films can support “topological metals” of the time-reversal invariant variety as well as time-reversal symmetry broken “Chern metals”
Summary
Topological phases have attracted much interest in recent years[1,2,3]. While there are a number of three-dimensional materials exhibiting topological properties[4], there are relatively few two-dimensional examples[5,6,7] aside from the well-known quantum Hall systems[8]. It is appreciated that three-dimensional pyrochlore iridates of the form R2Ir2O7, where R is a rare-earth element such as La, Y, or Eu may not have the correct electronic band structure features to support topological insulating states—namely that there is a (4-fold) band degeneracy at the Fermi energy protected by crystal symmetry[13,22,24]. This symmetry-protected gapless point at the Fermi energy precludes insulating states in the absence of crystal symmetry breaking and strongly disfavors the proposals[17,18,19,20,21,22,23] in this class of materials. If the system is relatively clean, the edge states will retain properties qualitatively similar to the corresponding insulating partner (either Z2 TI or CI) that would be obtained if the band structure were “deformed” in such a way to make the indirect gap positive while maintaining the positive direct gap
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