Commonly materials are classified as either electrical conductors or insulators. The theoretical discovery of topological insulators (TIs) in 2005 has fundamentally challenged this dichotomy. In a TI, spin-orbit interaction generates a non-trivial topology of the electronic band-structure dictating that its bulk is perfectly insulating, while its surface is fully conducting. The first TI candidate material put forward -graphene- is of limited practical use since its weak spin-orbit interactions produce a band-gap of ~0.01K. Recent reinvestigation of Bi2Se3 and Bi2Te3, however, have firmly categorized these materials as strong three-dimensional TI's. We have synthesized the first bulk material belonging to an entirely different, weak, topological class, built from stacks of two-dimensional TI's: Bi14Rh3I9. Its Bi-Rh sheets are graphene analogs, 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 TI with a 2400K band-gap.
@article{arxiv.1303.2193,
title = {Stacked topological insulator built from bismuth-based graphene sheet analogues},
author = {Bertold Rasche and Anna Isaeva and Michael Ruck and Sergey Borisenko and Volodymyr Zabolotnyy and Bernd Buchner and Klaus Koepernik and Carmine Ortix and Manuel Richter and Jeroen van den Brink},
journal= {arXiv preprint arXiv:1303.2193},
year = {2013}
}