Crossover of the three-dimensional topological insulator Bi2Se3 to the two-dimensional limit

The gapless surface states of topological insulators could enable quantitatively different types of electronic device. A study of the topological insulating Bi₂Se₃ thin films finds that a gap in these states opens up in films below a certain thickness. This in turn suggests that in thicker films, gapless states exist on both upper and lower surfaces.