Regensburg 2022 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 68: Focus Session: Time-Resolved Momentum Microscopy
O 68.4: Vortrag
Donnerstag, 8. September 2022, 16:15–16:30, H3
Electron dynamics after a spin- and valley-polarized electronic excitation in WS2 — •Lasse Münster1, Sarah Zajusch1, Raul Perea-Causin1, Samuel Brem1, Katsumi Tanimura1, Jens Güdde1, Yaroslav Gerasimenko2, Rupert Huber2, Ermin Malic1, Ulrich Höfer1, and Robert Wallauer1 — 1Fachbereich Physik, Philipps-Universität Marburg, Germany — 2Fachbereich Physik, Universität Regensburg, Germany
Atomically thin layers of TMDCs offer an ideal playground to study ultrafast electron dynamics. After optical excitation electrons scatter throughout the Brillouin zone to form a variety of excitonic states. We have shown that this formation process can be imaged by time-resolved momentum microscopy with tunable pump and high harmonic probe [1].
We recently incorporated a new pumping scheme, that allows us to excite the sample under an incident angle close to 0∘ with circularly polarized light. This results in an excitation, which is located purely within the K valley for one helicity and in the K’ valley for the other helicity and provides access to all possible scattering processes. In the case of an excitation at K, electron scattering to K’ and Σ is mediated by strong electron-phonon coupling with time constants of a few tens of femtoseconds. In addtion, we observe the formation of spin-forbidden excitons in the K valley and electron scattering towards Σ’. Both of these processes involve a spin-flip and are significantly slower (50 - 100 fs).
[1] R. Wallauer et al., Nano Lett. 21, 5867 (2021)