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O: Fachverband Oberflächenphysik

O 9: Ultrafast Electron Dynamics at Surfaces and Interfaces 2

O 9.7: Vortrag

Montag, 5. September 2022, 16:30–16:45, H3

Ultrafast phonon thermalization in a monolayer crystal — •Hyein Jung — Fritz-Haber-Institut der MPG

Understanding energy flow in semiconductors following a perturbation is key for future applications. Observing dynamic processes on their fundamental time scales enables studying energy transfer processes between intrinsic subsystems, and subsequently understanding the coupling between them. Here we study ultrafast lattice dynamics in monolayer WSe2, carried out using femtosecond (high-energy) electron diffraction (FED).

We studied the lattice response to laser excitation by probing laser-induced variations in Bragg peak intensities, which reflect changes in incoherent lattice vibrations (quantified by atomic mean squared displacements, MSD). We implement a novel approach to analyze such diffraction data, by which we disentangle element-specific vibrational responses in the sub-picosecond time domain.

Through this analysis, we observe a series of steps in the evolution of the lattice response through varying trends of the two elements (W, Se). These observations suggest a cascade of electron-phonon and phonon-phonon scattering processes occurring on short picosecond time scales. We interpret these by means of energy transfer between phonon groups using on ab-initio calculations of the partial phonon density of states phonon. These results demonstrate that our element-specific approach enables a deeper understanding of the cascade of e-ph and ph-ph energy transfer processes following excitation.