Excitons in twisted van der Waals bilayers: Internal structure and ultrafast dynamics

By probing internal 1s-2p transitions with phase-locked mid-infrared pulses, we reveal the internal structure and binding energy of photo-generated excitons in transition metal dichalcogenide bilayers. Furthermore, we trace how the twist angle precisely controls the ultrafast formation of interlayer excitons and tunes excitonic hybridization in hetero- and homobilayers, respectively.