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O: Fachverband Oberflächenphysik
O 108: Electron-Driven Processes at Surfaces and Interfaces
O 108.10: Vortrag
Donnerstag, 19. März 2020, 17:15–17:30, TRE Ma
Excitation of a CDW Amplitudon Mode in Indium Atomic Wires on Si(111) studied by Femtosecond Surface Electron Diffraction — Bernd Hafke1, Tobias WItte1, Christian Brand1, and •Michael Horn-von Hoegen1,2 — 1Fakultät Physik, Universität Duisburg-Essen — 2Center for Nanointegration Duisburg-Essen, CENIDE
The ground state of the Indium atomic wire system on Si(111) is Peierls distorted with periodicity doubling along and perpendicular to the wires, thus resulting in a (8×2) reconstruction. This low-temperature state comes with a metal to insulator transition, opening of a bandgap, and formation of a CDW and exhibits a by 0.1 eV lower energy than the metallic high-symmetry (4×1) state. Here, we report on the excitation of an amplitudon mode of the CDW system by impulsive optical excitation through an IR fs laser pulse under conditions of weak laser fluence < 1 mJ/cm2. The observed intensity oscillation in ultra-fast time resolved electron diffraction at a period of 1.4 ps can be described by a superposition of the two characteristic phonon modes, namely the soft rotational and soft shear mode at frequencies of 0.82 THz and 0.54 THz, respectively, which at laser fluences > 2 mJ/cm2 facilitate the systems non-thermally driven transition to the excited (4×1) state [Nature 544 (2017) 207].