Speaker
Description
The physical response of condensed matter is determined by the microscopic interactions between internal degrees of freedom, such as charge, spin, or lattice. Ultrafast methods provide insights into these interactions by studying a materials ultrafast nonequilibrium response, which helps us to understand how macroscopic material properties arise from oftentimes complex microscopic interactions. However, established ultrafast spectroscopy approaches spatially average over large sample areas, although materials are usually inhomogeneous on nanometer or even Angstrom length scales. Gaining comprehensive insight into the local ultrafast response of surfaces, molecules, and quantum materials, and correlating this with the spatially averaged global response, therefore requires new experimental tools that combine ultrafast temporal with ultrahigh spatial resolution.
Ultrafast scanning tunneling microscopy (USTM) has become a powerful and versatile tool for imaging ultrafast dynamics at surfaces with atomic-scale spatial resolution. One of the most promising approaches that has emerged in the past decade is THz-lightwave-driven STM (THz-STM). THz-STM utilizes broadband single-cycle THz pulses as a quasi-static bias voltage in STM. It combines the free-space illumination of optical radiation with the previous ideas of nonlinear rectification in tunnel junctions driven by AC electric fields. Here we show the conceptual principle of THz-STM and explain the technical aspects of the THz-STM setup we build in the last years at FHI. We highlight the system's flexibility and capabilities for future ultrafast microscopy and spectroscopy at atomic scales.
