The topological insulating materials offer conductive surface states that can be useful for quantum computing, catalysis, and other applications. In this recent work, we (Young, Chowdhury, Walter, Mele, Kane, and Rappe, under review, 2011) show that compressing the material strengthens the topological insulating state, while expanding the material eventually takes this behavior away completely. Using external pressure as a control parameter suggests general ways to strengthen this important physical effect.

Black: the solid is expanded; there is an ordinary band gap
Blue: moderate compression closes the gap; Dirac cone seen
Red: further compression opens a different kind of gap: the connectivity of the states gives exotic surface properties