Development of an Ultrafast Scanning Tunnelling Microscope

Using ultrafast techniques, the dynamics of electrons in bulk and two-dimensional condensed matter systems can be studied with femtosecond time resolution. However, diffraction limits the spatial resolution to dimensions comparable to the wavelength of the radiation employed. As a result, ultrafast optical techniques are not suitable for investigating electron dynamics within single nanostructures or molecules with atomic precision. On the other hand, scanning tunnelling microscopy probes steady-state electronic properties with atomic spatial resolution, exploiting the extreme directionality of quantum tunnelling currents arising when a metallic tip is brought to a nanometric distance from a conductive surface under an applied bias. The temporal resolution of conventional scanning tunnelling microscopy is worse than 1ns, due to the limited bandwidth of state-of-the-art electronics. To overcome this limitation, we propose to exploit the electric field of near-infrared single-cycle laser transients to coherently drive electron tunnelling across the junction of a scanning tunnelling microscope, potentially paving the wave for ultrafast experiment with an unprecented combination of sub-10fs temporal and atomic spatial resolution.