Berlin 2024 – scientific programme

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O: Fachverband Oberflächenphysik

O 54: Scanning Probe Microscopy: Light Matter Interaction at Atomic Scales I

O 54.1: Topical Talk

Wednesday, March 20, 2024, 15:00–15:30, MA 041

Ultrafast scanning tunneling microscopy as a local probe of femtosecond electron and coherent phonon dynamics — •Melanie Müller — Fritz Haber Institute, Berlin, Germany

Ultrafast scanning tunneling microscopy (USTM) has emerged as a powerful tool for imaging electronic and structural excitations at surfaces with angstrom spatial and femtosecond temporal resolution. THz-lightwave-driven STM (THz-STM) and optical photon-assisted STM (ph-STM) offer two approaches [1] to probe the dynamics of charge, orbital and lattice degrees of freedom at the atomic scale. While THz-STM uses single-cycle THz pulses to drive tunneling via classical rectification, ph-STM is based on photon absorption-induced tunneling. Both allow to probe coherent phonons (CPs) and ultrafast changes in the occupation and local density of electronic states (LDOS). CPs modulate the electronic structure of solids, and thus the electronic states involved in tunneling. Here we use ph-STM to probe CPs in ultrathin ZnO/Ag(111) via their coupling to an optical resonance that enhances photon-assisted tunneling [2]. On the other hand, THz-STM allows more direct access to the LDOS by quasi-static tunneling. We study the commensurate charge density wave (CDW) phase in 1T-TaS₂, and probe the photoinduced Mott collapse and coherent CDW amplitude motion with THz-STM. The ability to probe both ultrafast local atomic and electronic structure makes USTM unique for imaging spatially inhomogeneous nonequilibrium dynamics in strongly correlated materials at the atomic scale. [1] M. Müller, Prog. Surf. Sci. 100727 (2023) [2] S. Liu et al., Sci. Adv. abq5682 (2022)

Keywords: ultrafast STM; THz-STM; coherent phonons; ultrafast electron dynamics