Coherent dynamics of resonantly excited excitons in monolayers of transition metal dichalcogenides

Tomasz Jakubczyk; Miroslav Bartos; Lorenzo Scarpelli; Karol Nogajewski; Wolfgang Langbein; Marek Potemski; Jacek Kasprzak

doi:10.1117/12.2549229

27 February 2020 Coherent dynamics of resonantly excited excitons in monolayers of transition metal dichalcogenides

Tomasz Jakubczyk, Miroslav Bartos, Lorenzo Scarpelli, Karol Nogajewski, Wolfgang Langbein, Marek Potemski, Jacek Kasprzak

Author Affiliations +

Proceedings Volume 11278, Ultrafast Phenomena and Nanophotonics XXIV; 112781C (2020) https://doi.org/10.1117/12.2549229
Event: SPIE OPTO, 2020, San Francisco, California, United States

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.

Conference Presentation

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Tomasz Jakubczyk, Miroslav Bartos, Lorenzo Scarpelli, Karol Nogajewski, Wolfgang Langbein, Marek Potemski, and Jacek Kasprzak "Coherent dynamics of resonantly excited excitons in monolayers of transition metal dichalcogenides", Proc. SPIE 11278, Ultrafast Phenomena and Nanophotonics XXIV, 112781C (27 February 2020); https://doi.org/10.1117/12.2549229

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