GRK Colloquium:
Ulrich Höfer

Formation of Floquet-Bloch bands in solids
Periodic driving of electrons in solids by strong light fields can lead to the formation of Floquet- Bloch bands, i.e., sidebands separated by multiples of the driving frequency. The induced change of the electronic structure is one route to materials design by light. In 2009, Oka proposed that circularly polarized light can turn the semimetal graphene into a Chern insulator in this way. While transport experiments could so far not provide compelling evidence for the predicted anomalous Hall effect, time-resolved photoemission has clearly demonstrated the formation of Floquet-Bloch bands for several materials, including graphene. Moreover, with subcycle resolution, it has become possible to reveal their ultrafast build-up. These experiments show that Floquet sidebands emerge after a single optical cycle, concurrently with intraband acceleration of the electrons.
Venue: RUN auditorium