LAUSR

Shining a light on STM Whereas ultrafast light pulses can provide a window into the dynamics of some of the fastest processes in condensed matter systems, scanning tunneling microscopy (STM) provides snapshots of atomic-scale spatial resolution of surfaces. By irradiating the tunnel junction with carrier-enveloped, phase-stabilized femtosecond light pulses, Garg and Kern effectively combined the two methods to demonstrate a technique capable of both high temporal and high spatial resolution of the elementary processes in matter (see the Perspective by Aiello). By tracking the decay dynamics of plasmonic excitations on the surface of gold nanorods, they illustrate the power of the technique for the tracking and control of ultrafast electronic processes on the atomic scale. Science, this issue p. 411; see also p. 368 Ultrafast light pulses combined with scanning tunneling microscopy can track electronic processes with high spatial and temporal resolution. Nanoelectronic devices operating in the quantum regime require coherent manipulation and control over electrons at atomic length and time scales. We demonstrate coherent control over electrons in a tunnel junction of a scanning tunneling microscope by means of precise tuning of the carrier-envelope phase of two-cycle long (<6-femtosecond) optical pulses. We explore photon and field-driven tunneling, two different regimes of interaction of optical pulses with the tunnel junction, and demonstrate a transition from one regime to the other. Our results show that it is possible to induce, track, and control electronic current at atomic scales with subfemtosecond resolution, providing a route to develop petahertz coherent nanoelectronics and microscopy.