Switching on surface conduction in a topological insulator

The protected surface conduction of topological insulators is in high demand for the next generation of electronic devices. What is needed to move forward are robust settings where topological surface currents can be controlled by simple means, ideally by the application of external stimuli. Surprisingly, this direction is only little explored. In this work we demonstrate that we can boost the surface conduction of a topological insulator by both light and electric field. This happens in a fully controlled way, and the additional Dirac carriers exhibit ultra-long lifetimes. We provide a comprehensive understanding, namely that carriers are injected from the bulk to the surface states across an intrinsic Schottky barrier. We expect this mechanism to be at play in a broad range of materials and experimental settings.