Commonly, materials are classified as either electrical conductors or insulators. The theoretical discovery of topological insulators has fundamentally challenged this dichotomy. In a topological insulator, the spin–orbit interaction generates a non-trivial topology of the electronic band structure dictating that its bulk is perfectly insulating, whereas its surface is fully conducting. The first topological insulator candidate material put forward—graphene—is of limited practical use because its weak spin–orbit interactions produce a bandgap of ~ 0.01 K. Recent reexaminations of Bi2Se3 and Bi2Te3, however, have firmly categorized these materials as strong three-dimensional topological insulators. We have synthesized the first bulk material belonging to an entirely different, weak, topological class, built from stacks of two-dimensional topological insulators: Bi14Rh3I9. Its Bi–Rh sheets are graphene analogues, but with a honeycomb net composed of RhBi8 cubes rather than carbon atoms. The strong bismuth-related spin–orbit interaction renders each graphene-like layer a topological insulator with a 2,400 K bandgap.
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We acknowledge the help of S. Thirupathaiah, T. Kim and J. Maletz at the ARPES beamline and the grants: BO 1912/3-1, BO 1912/2-2 and ZA 654/1-1. We thank M. Kaiser and A. Gerisch for contributions in solving the crystal structure. We are indebted to ZIH TU Dresden for the provided computational facilities.
The authors declare no competing financial interests.
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Rasche, B., Isaeva, A., Ruck, M. et al. Stacked topological insulator built from bismuth-based graphene sheet analogues. Nature Mater 12, 422–425 (2013) doi:10.1038/nmat3570
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