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Proceedings Paper

Coherent dynamics of resonantly excited excitons in monolayers of transition metal dichalcogenides
Author(s): Tomasz Jakubczyk; Miroslav Bartos; Lorenzo Scarpelli; Karol Nogajewski; Wolfgang Langbein; Marek Potemski; Jacek Kasprzak
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Paper Abstract

We investigate dynamics of resonantly excited excitons in single-layers of MoSe2 and WS2 down to 4.5K. To this end, we measure the delay dependence of the heterodyne four-wave mixing (F M) amplitude induced by three, short laser pulses. This signal depends not only on the population of optically active excitons, which affects the absorption of the probe, but also on the population of optically inactive states, by interaction-induced energy shift, influencing the refractive index experienced by the probe. As such, it offers insight into density dynamics of excitons which do not directly couple to photons. Reproducing the coherent signal detected in amplitude and phase, the FWM delay dependence is modeled by a coherent superposition of several exponential decay components, with characteristic time constants from 0.1 picosecond up to 1 nanosecond. With increasing excitation intensity and/or temperature, we observe strong interference effects in the FWM field amplitude, resulting in progressively more complex and nonintuitive signal dynamics. We attribute this behaviour to increasingly populated exciton dark states, which change the FWM field phase by the relative effect on absorption and refractive index. We observe that exciton recombination occurs on a significantly longer timescale in WS2 with respect to MoSe2, which is attributed to the dark character of exciton ground state in the former and the bright in the latter.

Paper Details

Date Published: 27 February 2020
PDF: 10 pages
Proc. SPIE 11278, Ultrafast Phenomena and Nanophotonics XXIV, 112781C (27 February 2020); doi: 10.1117/12.2549229
Show Author Affiliations
Tomasz Jakubczyk, Univ. Grenoble Alpes, CNRS, Grenoble INP, Institut Néel (France)
Univ. of Basel (Switzerland)
Miroslav Bartos, Lab. National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL (France)
Brno Univ. of Technology (Czech Republic)
Lorenzo Scarpelli, Macquarie Univ. (Australia)
Karol Nogajewski, Lab. National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL (France)
Univ. of Warsaw (Poland)
Wolfgang Langbein, Cardiff Univ. (United Kingdom)
Marek Potemski, Lab. National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL (France)
Univ. of Warsaw (Poland)
Jacek Kasprzak, Univ. Grenoble Alpes, CNRS, Grenoble INP, Institut Néel (France)


Published in SPIE Proceedings Vol. 11278:
Ultrafast Phenomena and Nanophotonics XXIV
Markus Betz; Abdulhakem Y. Elezzabi, Editor(s)

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