Dr Melanie Muller, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin,Germany
Recent advances in coupling ultrafast optical and terahertz (THz) pulses to low-temperature scanning tunneling microscopes (STM) have opened new
frontiers for probing light-driven processes with simultaneous femtosecond temporal and angstrom spatial resolution. In this talk, I will present two
approaches based on optical photon-driven STM (phSTM) and THz-lightwave-driven STM (THz-STM) to explore ultrafast dynamics at the nanoscale.
First, using phSTM with plasmonic tunnel junctions,we investigate coherent phonon dynamics in ultrathin ZnO/Ag(111), demonstrating coherent
phonon spectroscopy with nanometer resolution. I will discuss how optical resonances and localized plasmons mediate the excitation and detection of these
ultrafast lattice vibrations on the nanoscale.
Second, we apply THz-STM with femtosecond photoexcitation to study a THz-induced metastable state in the layered charge density wave material 1T-TaS₂. We resolve the dynamics of this state in real space and time,
and trace the CDW amplitude mode and a previously unobserved interlayer shear mode across individual CDW superlattice sites near a defect.
These results demonstrate the power of ultrafast STM to resolve non-equilibrium phenomena with unprecedented resolution, providing direct access to local excited-state dynamics and opening new
pathways for exploring the ultrafast response of quantum materials at their fundamental time and length scales.