Berlin 2024 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 54: Scanning Probe Microscopy: Light Matter Interaction at Atomic Scales I
O 54.2: Vortrag
Mittwoch, 20. März 2024, 15:30–15:45, MA 041
THz waveform optimization for ultrafast time-domain spectroscopy in the scanning tunneling microscope — Shaoxiang Sheng1,2, Kurt Lichtenberg1, Felix Huber1, Johannes Schust1, Li Chen3, Susanne Baumann1, and •Sebastian Loth1 — 1University of Stuttgart, Institute for Functional Matter and Quantum Technologies, Stuttgart, Germany — 2Max Planck Institute for Solid State Research, Stuttgart, Germany — 3Program in Materials Science and Engineering, University of California San Diego, La Jolla, CA, USA
Exciting the tunnel junction of a scanning tunneling microscope (STM) with sub-cycle THz pulses enables ultrafast spectroscopy of electron, phonon and molecular motion dynamics on surfaces with atomic spatial and sub-picosecond temporal resolution. THz pulses coupled to the STM tip induce short bursts of electron tunneling that are used to sample the ultrafast dynamics. Hence, the sensitivity and time resolution achievable with this technique critically depends on the quality of the THz pulse's electric-field waveform. We use electro-optic sampling of tip-scattered THz light (s-EOS) from the STM tip and pulse-pulse correlation measurements of the THz-induced tunnel current to characterize the shape of the THz electric field in the tunnel junction. Comparison with finite-element modeling of the THz near field identifies reflections and spectral distortions that originate from THz surface plasmon propagation along the STM tip. We find an optimized tip geometry that flattens the electric field waveform in the tunnel junction and enables accurate time-domain spectroscopy.
Keywords: scanning tunneling microscopy; terahertz; pump probe spectroscopy; terahertz plasmonics