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O: Fachverband Oberflächenphysik

O 18: Poster Focus Session Ultrafast Electron Microscopy at the Space-Time Limit

O 18.7: Poster

Montag, 17. März 2025, 18:00–20:00, P2

Spatio-Temporal Electron Propagation Dynamics in Au/Fe/MgO(001) in Nonequilibrium — Markus Heckschen¹, Yasin Beyazit¹, Elaheh Shomali¹, Florian Denizer¹, J. Jayabalan¹, Ping Zhou¹, Detlef Diesing², Markus Gruner¹, Rossitza Pentcheva¹, Axel Lorke¹, Björn Sothmann¹, and •Uwe Bovensiepen¹ — ¹University of Duisburg-Essen, Faculty of Physics and CENIDE, 47048 Duisburg — ²University of Duisburg-Essen, Faculty of Chemistry, 45141 Essen

Since the mean free path of hot electrons is only a few nanometer, insights into the spatio-temporal electron dynamics are desired for the analysis of ultrafast microscopy. We determine the energy-dependent electron propagation time through epitaxial Au/Fe(001) as a function of Au layer thickness [1] by femtosecond time-resolved two-photon photoemission spectroscopy at energies 0.5-2.0 eV above E_F. By combining real-time time-dependent density functional theory and microscopic electron transport simulations we identify ballistic transport of minority electrons of the optically excited electron population. At lower energy, superdiffusive transport with 1-4 scattering events dominates. The effective electron velocity accelerates from 0.3 to 1 nm/fs with an increase in the Au layer thickness from 10 to 100 nm which is explained by electron transport that becomes preferentially aligned with the interface normal for thicker Au layers. On this basis the electron momentum or energy can be selected by the choice of the propagation layer thickness. We acknowledge funding by the DFG through SFB 1242. [1] Heckschen et al., PRX ENERGY 2, 043009 (2023).

Keywords: non-equilibrium electron dynamics; time-resolved photoelectron spectroscopy; buried interfaces / media; ballistic and superdiffusive electron transport