Ultrafast Photocurrents in a topological insulator

Photocurrents in topological materials have been associated with topological properties of the electronic bands, such as the Berry connection. However, despite some experimental demonstrations, it has remained unclear what part the topology actually plays in the process. In this talk I will discuss our use of time- and angle-resolved photoemission spectroscopy (trARPES) to resolve photocurrents in the excited electronic states of a topological insulator. By analyzing the rise times of the population following the optical excitation, we gained a complete view of the occupied and unoccupied electronic states, and how they are coupled by the light. Our work provides a microscopic understanding of how to control photocurrents in materials with spin-orbit coupling and broken inversion symmetry, and paves the way to control of currents in topological states. I will also briefly describe trARPES experiments on a magnetic Weyl semimetal.