Subcycle optical microscopy with Angstrom-scale resolution

We introduce a novel contrast mechanism in near-field microscopy which allows for all-optical atomic-scale microscopy with subcycle temporal resolution. To this end, we combine near-field microscopy with ultrahigh vacuum, low temperatures and sub-nanometer tip tapping amplitudes. On these scales, a surprisingly efficient non-classical near-field response occurs, which follows the vector potential of light and is strictly confined to atomic length scales. This ultrafast signal features an optical phase delay of ~π/2 and facilitates tracking of tunnelling dynamics. Our method reveals nanoscale defects and captures current transients on semiconducting van-der-Waals materials with subcycle sampling, allowing us to record the quantum flow of electrons in conductive and insulating quantum materials at ultimate spatiotemporal scales.