Insulator to Order

摘要

Unlike simple band-gap insulators, bulk topo-logical insulators permit movement of charges on their boundaries while acting as insulators in their interior. Both types of insulators usually occur in different families of compounds. Now, Xu et al. (p. 560, published online 31 March; see the Perspective by Fiete) can promote transition between a direct band gap and topological insulator within a bulk bismuth-containing solid by changing the relative ratio of its sulfur and selenium content.