Regensburg 2019 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 97: Ultrafast Electron Dynamics at Surfaces and Interfaces III

O 97.6: Vortrag

Freitag, 5. April 2019, 11:45–12:00, H16

Relaxation of electronically confined states from Master Equation with first-principles-derived rates — •Peter Kratzer, Maedeh Zahedifar, and Sebastian Schreiber — Fakultät für Physik, Universität Duisburg-Essen

Atomically thin films of Pb on Si(111) provide an experimentally tunable system comprising both dispersive bands with metallic character and confined, thickness-dependent quantum well states. The lifetime of excited electrons in Pb films is limited by both electron-electron (e-e) and electron-phonon (e-ph) scattering. We employ the description by a Master equation for the electronic occupation numbers to analyse the relative importance of both scattering mechanisms. The electronic and phononic band structures, as well as the matrix elements for electron-phonon coupling within deformation potential theory were obtained from density functional calculations. The contribution of impact ionization processes to the lifetime is estimated from the imaginary part of the electronic self-energy calculated in the GW approximation. By numerically solving the rate equations for the occupations of the Pb-derived electronic states coupled to phononic heat baths, we can follow the distribution of the electronic excitation energy to the various modes of Pb lattice vibrations. While e-e scattering is the dominant relaxation mechanism, we demonstrate that the e-ph scattering is highly mode-selective, with a large contribution from surface phonons. The time scales extracted from the simulations are compared to experimental data from time-resolved pump-probe experiments.

Funding: DFG, SFB1242

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