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O: Fachverband Oberflächenphysik
O 5: Scanning Probe Microscopy: Light-Matter Interactions at the Atomic Scale I
O 5.6: Vortrag
Montag, 17. März 2025, 11:45–12:00, H6
Charge Transfer in Lightwave-Driven Scanning Tunneling Microscopy — •Nils Krane, Jonas Allerbeck, Laric Bobzien, S. Eve Ammerman, and Bruno Schuler — Empa - nanotech@surfaces Laboratory, 8600 Dübendorf, Switzerland
Lightwave-driven STM is a promising technique for exploring ultrafast charge-state dynamics at nanoscale. The tip electrode of the STM provides spatial resolution at the single-atom level, while single-cycle lightwave pulses supply an ultrafast voltage source at GHz to multi-THz frequencies that injects charge carriers to the system. In contrast to optical far-field measurements, the STM tip interacts with the investigated system also between the pulses where the applied voltage is low. This allows for ultrafast back tunneling of electrons from an excited charge state via discharging to the tip electrode, resulting in zero net current. Equal magnitude of forward and backward tunneling hence quenches the time-integrated charge rectification and imposes a major challenge on investigating ultrafast nanoscale charge dynamics. In this talk, I discuss the consequences of back tunneling for lightwave-driven STM and time-domain pump-probe techniques, at the example of picosecond charge-state lifetimes related to selenium vacancies in WSe2 studied with THz-STM. I outline pathways to overcome this challenge by utilizing effects such as the Franck-Condon blockade or spin multiplicity for the promotion of unidirectional charge transport. A theoretical model based on the master equation, accurately reproduces the time-dependent tunneling processes observed in the experiments.
Keywords: ultrafast scanning probe microscopy; THz-STM; pump-probe STM; field-driven tunneling; Franck-Condon blockade