Topological insulators: Chemists join in

Topological insulators (TI) are small-bandgap semiconductors in which there is a small difference in electronegativity between the ions whose orbitals typically contribute to the conduction band and the ions whose orbitals typically contribute to the valance band. The orbitals therefore mix, resulting in a continuous distribution of electron energy states rather than a bandgap. In TIs the presence of strong spin-orbit coupling largely unmixes these states, creating a bandgap and bulk semiconducting behaviour. The synthesis and characterization of Bi₁₄Rh₃I₉, a so-called weak topological insulator, have much to offer to the field. This material can be idealized into something as simple as heavy graphene, a material that both chemists and physicists can easily relate to.