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Possible Three-Dimensional Topological Insulator in Pyrochlore Oxides

National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 2, Umezono 1-1-4, Tsukuba, Ibaraki 305-8568, Japan
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Symmetry 2020, 12(7), 1076; https://doi.org/10.3390/sym12071076
Received: 25 May 2020 / Revised: 9 June 2020 / Accepted: 12 June 2020 / Published: 1 July 2020
(This article belongs to the Special Issue Vortex, Topology and Singularity in Quantum Systems)
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. View Full-Text
Keywords: pyrochlore oxide; band calculation; flat band; spin–orbit interaction; topological insulator pyrochlore oxide; band calculation; flat band; spin–orbit interaction; topological insulator
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Hase, I.; Yanagisawa, T. Possible Three-Dimensional Topological Insulator in Pyrochlore Oxides. Symmetry 2020, 12, 1076.

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