SurfaceScience21 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 79: Poster Session VI: Ultrafast electron dynamics at surface and interfaces II
O 79.2: Poster
Mittwoch, 3. März 2021, 13:30–15:30, P
Dynamic screening of quasiparticles in WS2 monolayers — •Stefano Calati1,2, Qiuyang Li3, Xiaoyang Zhu3, and Julia Stähler1,2 — 1Department of physical chemistry, Fritz-Haber-Institut der MPG, Berlin — 2Institut für Chemie, Humboldt-Universität zu Berlin — 3Department of Chemistry, Columbia University, New York
The low dimensional nature of TMDCs and the resulting reduced screening influence their non-equilibrium optical properties, as dynamic screening by photoexcited quasiparticles governs the transient response. Here, we investigate the respective roles of excitons and quasi-free carriers on the dynamic response of WS2 monolayers on SiO2. We find drastic changes in the reflectivity/transmittance contrast upon photoexcitation. The main observation is a pump photon energy-dependent blue/red shifts of the neutral exciton. Based on a phenomenological model, we disentangle the different impact of excitons and free carriers on the renormalization of the quasi-free-particle band gap and exciton binding energy. This work unravels and quantifies the competition and interplay of the multiple electronic and thermal processes contributing to the recovery of the system upon photoexcitation.