Stacked topological insulator built from bismuth-based graphene sheet analogues

TL;DR

This paper reports the synthesis of a novel bulk material composed of stacked bismuth-based graphene analogues, which are topological insulators with a significant band-gap, advancing the understanding of layered topological insulators.

Contribution

It introduces a new class of weak topological insulators built from stacked two-dimensional TIs with bismuth-based honeycomb layers, expanding the material landscape of topological insulators.

Findings

First bulk material of its kind with stacked 2D TIs

Each layer exhibits a large 2400K band-gap

Material built from RhBi8-cube honeycomb structures

Abstract

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.