Condensed Matter Seminar: Optically probing and manipulating correlated states in magic angle twisted bilayer graphene

Optically probing quantum materials offers a versatile way to access information about the energetics and symmetry properties of the electrons in the materials. The flat-band electrons in twisted bilayer graphene are particularly interesting to investigate this way, because they host an array of strongly correlated states with different symmetries. However, the bandwidths and energy gaps in graphene-based moire systems are typically small, making it difficult to probe them with conventional optics. In this talk, I will show the effects of near infra-red illumination on the transport properties of magic-angle twisted bilayer graphene, focusing on the anomalous Hall effect. I will show that circularly polarized light changes the transverse resistance in a way that enables probing the magnetic susceptibility of the system. Furthermore, I will show evidence of light-induced domain dynamics in the anomalous Hall state, which enables studying the critical behavior of the anomalous Hall transition. The large effects we observed suggest that remote bands are important for fully understanding the light-matter interaction in this system, and open the door to optical control of orbital magnetism in van der Waals materials.