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O: Fachverband Oberflächenphysik
O 30: Focus Session: Phonon Polaritons: Opportunities for THz Nanooptics I
O 30.2: Hauptvortrag
Dienstag, 13. März 2018, 11:00–11:30, HE 101
Femtosecond nanoscopy of collective excitations in semiconductors — •Markus A. Huber1, Fabian Mooshammer1, Markus Plankl1, Leonardo Viti2, Fabian Sandner1, Miriam S. Vitiello2, Tyler L. Cocker1, and Rupert Huber1 — 1University of Regensburg, 93040 Regensburg, Germany — 2NEST CNR, 56127 Pisa, Italy
Far-field multi-THz studies are intrinsically limited in their spatial resolution to the scale of the probing wavelength by diffraction. Scattering-type scanning near-field optical microscopy (s-SNOM) overcomes this limitation by utilizing the electric near fields below the apex of a sharp metallic tip. Using ultrafast multi-THz s-SNOM we probe the transient, nanoscale dielectric functions of materials upon photoexcitation by femtosecond near-infrared pulses. We apply the system to investigate the plasmonic response in a single InAs nanowire, where ultrafast near-field tomography reveals the < 50 fs build-up of a surface depletion layer. Additionally, we resolve the oscillating electric near field on the wire surface directly in the time domain and demonstrate a spatial and temporal resolution of 10 nm and 10 fs, respectively. We also show that the insulator-to-metal phase-switching behavior in strained VO2 nanobeams can be predicted via the local contrast of the pump-probe response at room temperature. Finally, we trace the evolution of photo-activated surface phonon-plasmon polaritons in custom-tailored black phosphorus/SiO2 heterostructures on the nanoscale. These polaritons feature key elements for ultrafast control: ≈ 50 fs switch-on times and constant energy and momentum.