Abstract
A Kene–Mele-type nearest-neighbor tight-binding model on a pyrochlore lattice is known to be a topological insulator in some parameter region. It is an important task to realize a topological insulator in a real compound, especially in an oxide that is stable in air. In this paper we systematically performed band structure calculations for six pyrochlore oxides A2B2O7 (A = Sn, Pb, Tl; B = Nb, Ta), which are properly described by this model, and found that heavily hole-doped Sn2Nb2O7 is a good candidate. Surprisingly, an effective spin–orbit coupling constant λ changes its sign depending on the composition of the material. Furthermore, we calculated the band structure of three virtual pyrochlore oxides, namely In2Nb2O7, In2Ta2O7 and Sn2Zr2O7. We found that Sn2Zr2O7 has a band gap at the k = 0 (Γ) point, similar to Sn2Nb2O7, though the band structure of Sn2Zr2O7 itself differs from the ideal nearest-neighbor tight-binding model. We propose that the co-doped system (In,Sn)2(Nb,Zr)2O7 may become a candidate of the three-dimensional strong topological insulator.
Highlights
IntroductionNon-trivial states in materials have been paid much attention in the last decades
Non-trivial states in materials have been paid much attention in the last decades.Among them, topological insulators (TIs) have attracted attention, from a basic and from an application point of view
In previous papers [14,15,16] we have shown that six pyrochlore oxides A2 B2 O7 (A = Sn, Pb, Tl; B = Nb, Ta) have band structures that are well described in the Guo and Franz (GF) model
Summary
Non-trivial states in materials have been paid much attention in the last decades. Topological insulators (TIs) have attracted attention, from a basic and from an application point of view. In TI, while the bulk is insulating, the surface has a metallic state Since this surface state is robust against perturbations that do not violate the time reversal symmetry, it has been pointed out that it can be applied to a quantum computing device. Considering such applications, the material is desired to be three-dimensional and stable in the air, namely oxide.
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