Optical control of electrons in a Floquet topological insulator

Light-dressed materials offer a route to generating electronic properties that differ from those of materials at equilibrium. The resulting band structures can host distinct quantum and topological phenomena. So far, optical control of charge within a light-dressed band structure has remained elusive. Here we demonstrate optical control of electrons in light-dressed graphene. By focusing circularly polarized femtosecond laser pulses at 1,550 nm on monolayer graphene, we generate a Floquet topological insulator. With a phase-locked second-harmonic field, we dynamically control electrons in this state, a technique we call harmonic Floquet spectroscopy. We observe photocurrent circular dichroism, an all-optical anomalous Hall effect and valley-polarized currents. The photocurrents show strong subcycle phase sensitivity, suggesting a route to ultrafast control in topological electronics, spectroscopy and attosecond physics in quantum materials.