Berlin 2024 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 13: Ultrafast Electron Dynamics at Surfaces and Interfaces II
O 13.6: Vortrag
Montag, 18. März 2024, 16:30–16:45, MA 041
Electron-phonon coupling in ultrathin Pb films on Si(111): Where the heck is the energy? — •Mohammad Tajik1, Tobias Witte1, Christian Brand1, Laurenz Rettig2, Björn Sothmann1, Uwe Bovensiepen1, and Michael Horn-von Hoegen1 — 1Department of Physics, Universität Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany — 2Department of Physical Chemistry Fritz Haber Institute Faradayweg 4-6 14195 Berlin Germany
In this work, we studied the heat transfer from electron to phonon subsystem within a five monolayer thin epitaxial Pb film on Si(111) upon fs-laser excitation. The response of the electron subsystem was determined using time-resolved photoelectron spectroscopy (tr-PES) while the lattice excitation was measured by means of the Debye-Waller effect in time-resolved reflection high-energy electron diffraction (tr-RHEED). The electrons lose their heat in less than 0.7 ps while the lattice temperature rises slowly in 3.5 to 8 ps. This raises the question where is the energy hidden for 3-7 ps? Within a three-temperature model we used three heat baths, namely electrons, high-frequency and low-frequency phonon modes to simulate the observations. We propose that the hidden energy is transiently stored in high-frequency phonon modes at the zone boundary for which the tr-RHEED is insensitive and which are excited in less than 0.7 ps. The excitation of low-frequency acoustic phonons, i.e., thermalization of the lattice is facilitated through anharmonic phonon-phonon interaction.
Keywords: Lattice dynamics; electron dynamics; tr- PES; tr- RHEED; three temperature model