Regensburg 2025 – scientific programme
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O: Fachverband Oberflächenphysik
O 57: Ultrafast Electron Dynamics I
O 57.8: Talk
Wednesday, March 19, 2025, 12:30–12:45, H2
Momentum-resolved valleytronic dynamics in TMDC monolayers — •Sarah Zajusch1, Lasse Münster2, Marcel Theilen1, Marleen Axt1, Yaroslav Gerasimenko2, Jens Güdde1, Robert Wallauer1, and Ulrich Höfer1,2 — 1Fachbereich Physik, Philipps-Universität Marburg — 2Fachbereich Physik, Universität Regensburg
The lack of inversion symmetry allows to access the valley degree of freedom in TMDC materials. With circular polarized light, time-resolved momentum microscopy enables us to trace the formation of a rich variety of bright and dark excitons typical for these materials on an ultrafast timescale and throughout the whole Brillouin zone.
We performed measurements on both MoSe2 and WS2. In WS2, we observe a valley depolarization at room temperature within 100 fs, whereas in MoSe2, this happens on a slower timescale, with a slight polarization that is still visible long after 100 fs. There are mainly two proposed leading mechanisms for this relaxation process, exciton-phonon scattering and electron-hole exchange interaction, which are differently pronounced in W- and Mo-based TMDCs due to the differences in their excitonic energy landscapes. As the ultrafast formation of dark KK’- and KΣ-excitons in WS2 shows, mainly exciton-phonon scattering contributes to the valley relaxation here. This process is strongly temperature-dependent.
Keywords: ARPES; Momentum Microscopy; TMDC; WS2; MoSe2