Science http://doi.org/xks (2014)

Quantum spin Hall insulators form a class of materials that are insulating in the bulk, but have conducting edge states. As topological protection prevents backscattering in such states, spin and charge transport should occur without dissipation, which could be used to create low-power devices. Xiaofeng Qian and co-workers have now proposed a transistor that operates by switching the topological behaviour of these materials on and off.

Two-dimensional transition metal dichalcogenides consist of three layers, which can be stacked in a number of ways. Using first-principles calculations, Qian et al. predicted that for one particular type of stacking, a range of these materials should be quantum spin Hall insulators. They also predicted that moderate electric fields would transform them into ordinary insulators, destroying the edge states.

This electric-field-induced topological phase transition could be used to create transistors: in an 'on' state, current would flow without dissipation through edge states, whereas applying an electric field would turn the device 'off' as there would be no conducting channels. The current could then be increased simply by adding more layers. This proposed device is termed a van der Waals heterostructured topological field effect transistor.