Regensburg 2025 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 5: Scanning Probe Microscopy: Light-Matter Interactions at the Atomic Scale I

O 5.5: Vortrag

Montag, 17. März 2025, 11:30–11:45, H6

Spatial coherent phonon spectroscopy on 2H-MoTe₂ using THz-STM — •Vibhuti Rai, Junyoung Sim, Florian Faaber, Sergey Trishin, Nils Bogdanoff, Tom Seifert, Tobias Kampfrath, Christian Lotze, and Katharina J. Franke — Freie Universität Berlin, Department of Physics, Arnimallee 14,14195 Berlin, Germany

Scanning tunneling microscopy (STM) offers subnanometer spatial resolution. However, it lacks the temporal resolution required to investigate the dynamics of various elementary excitations such as phonons. By integrating STM with a pump-probe scheme that utilizes two terahertz (THz) pulses acting as transient bias voltages, subpicosecond time resolution can be achieved [1,2]. Here, we demonstrate that our custom-built THz setup, combined with an STM operating at 5K in an ultra-high vacuum, can be used to excite and detect lattice vibrations on the surface of 2H-MoTe₂. The time-resolved spectrum shows a long-lasting oscillatory signal that is sensitive to surface defects [3,4]. Fourier analysis reveals the presence of two prominent excitation modes. We correlate the excited modes with coherent phonons. The spatial variation of such coherent phonon spectroscopy further reveals that one of the two excited modes are enhanced by the surface defects.

[1] Cocker, et al. Nat. Photon. 7, 620-625 (2013)

[2] Yoshida et al. ACS Photonics 6, 6, 1356-1364 (2019)

[3] Liu et al. Sci. Adv. 8, eabq5682 (2022)

[4] Roelcke et al. Nat. Photon. 18, 595-602 (2024)

Keywords: Scanning tunnelling microscopy; Coherent phonon spectroscopy; THz excitations; Time-resolved measurements