Aharon Kapitulnik : Optical studies of gyrotropic MATBG

Flat bands in graphene-based moiré structures host a wide range of emerging strongly correlated and topological phenomena. Optically probing and controlling them can reveal important information such as symmetry and dynamics, but have so far been challenging due to the small energy gap compared to optical frequencies. In this talk we focus on the optical interrogation of a stack of magic angle twisted bilayer graphene (MATBG) and monolayer WSe2 device, which clearly exhibits orbital magnetism and associated anomalous Hall effects (AHE) near select moiré integer fillings. Circular photogalvanic effect (CPGE) measurements above the magnetic transitions reveal a finite response as a function of band filling, confirming the alluding to the finite Berry connection embedded in the band structure.  At low temperatures we show that the AHE phases, such as hysteresis and amplitude, can be controlled by circularly polarized light. By modulating the light helicity, we observe periodic modulation of the transverse resistance in a wide range of fillings, indicating light induced orbital magnetization through an anomalously large inverse Faraday effect associated with the flat band.