Berlin 2024 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 30: Ultrafast Phenomena II
HL 30.1: Talk
Wednesday, March 20, 2024, 10:00–10:15, EW 015
Ultrafast coherent exciton dynamics and manybody interactions in a WS2 monolayer — •Daniel Timmer1, Moritz Gittinger1, Daniel Lünemann1, Sven Stephan1,2, Martin Silies1,2, Antonietta De Sio1, and Christoph Lienau1 — 1University of Oldenburg, Germany — 2University of Applied Sciences Emden, Germany
Monolayers of transition metal dichalcogenides (TMDCs) are quantum materials with fascinating optoelectronic properties. In particular, valleytronic applications are exploiting the spin-selectivity that is provided by the valley pseudospin and large energy splitting between A and B excitons due to strong spin-orbit coupling. However, manybody interactions lead to rapid valley depolarization. In particular, exchange interactions lead to a mixing of A and B excitons. We use ultrafast pump-probe and two-dimensional electronic spectroscopy (2DES), the ideal tool to investigate coherent couplings and manybody interactions in semiconductors, to directly probe these A-B exciton interactions in a monolayer of WS2. We observe the signatures of coherent couplings between the A and B excitons, cross-peaks in the 2DES maps. The associated coherent Rabi oscillations with ~11.5-fs period are also resolved. In addition, the 2DES data gives detailed insight into the formation of manybody interactions on a tens of fs timescale. The observed coherent couplings are likely reflecting a Dexter-type intervalley exchange interaction. Broadband ultrafast spectroscopy with sufficiently high time-resolution proofs therefore essential in directly probing the coherent quantum dynamics in the time domain.
Keywords: transition metal dichalcogenides; Rabi oscillations; two-dimensional electronic spectroscopy; manybody interactions; monolayer WS2