With the rapid advancement of attosecond science, the intrinsic timescale of electronic dynamics in atoms, molecules and solids can now be accessed. Integrating attosecond techniques with conventional scanning tunneling microscopy (STM) has the potential to enable simultaneous ångström-attosecond resolution. Here, we present our theoretical and experimental studies on the physical dynamics of attosecond STM.
Because of the lack of appropriate theory models, we establish a new strong-field theory that successfully accounts for all regimes of laser-assisted STM. We show that the famous three-step model of attosecond science emerges in the strong-field regime and also introduce a new parameter which governs the physics in the tunneling gap junction. In our experiment, we use a two-color femtosecond laser to generate and observe attosecond current bursts. We demonstrate for the first time that the direction of the laser-induced attosecond currents in STM can be controlled with the phase of light, in agreement with our theory predictions. This advance opens the door to study ultrafast electronic dynamics in STM junctions and will provide new insights into attosecond-resolved electron dynamics in molecules and nanostructures.