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Disputation Daniela Zahn

13.05.2022 | 14:30
Thema der Dissertation:
Ultrafast lattice dynamics and microscopic energy flow in ferromagnetic metals and in an anisotropic layered semiconductor
Abstract: In this thesis, femtosecond electron diffraction was employed to study several technologically relevant materials: the layered semiconductor black phosphorus, the 3d ferromagnets iron, cobalt, and nickel, and the 4f ferromagnets terbium and gadolinium. The talk focuses on two topics: lattice dynamics in black phosphorus and ultrafast energy flow in 3d ferromagnets.
Black phosphorus exhibits a peculiar structure with in-plane anisotropy. Here, we use femtosecond electron diffraction to access the lattice response to laser excitation, which is found to be characterized by pronounced non-thermal phonon distributions. Our results yield insights into both electron-phonon and phonon-phonon coupling and provide pathways to control the timescale of lattice thermalization in black phosphorus.
The 3d ferromagnets iron, cobalt, and nickel exhibit ultrafast demagnetization on timescales of hundreds of femtoseconds following laser excitation. Here, three subsystems contribute to the ultrafast response: electrons, spins, and the lattice. We employ experimentally measured lattice responses to study the ultrafast energy flow between these subsystems. With energy-conserving ASD simulations, a quantitative and consistent description of this microscopic energy flow is achieved. In addition, a non-thermal behavior of the spin system is observed in the simulations, showing that thermal descriptions cannot capture the full non-equilibrium dynamics in magnetic materials.

Zeit & Ort

13.05.2022 | 14:30

Hörsaal B (0.1.01)
Fachbereich Physik, Arnimallee 14, 14195 Berlin