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

Research output: Chapter in Book/Report/Conference proceedingConference proceeding contributionpeer-review

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.

Original languageEnglish
Title of host publicationUltrafast Phenomena and Nanophotonics XXIV
EditorsMarkus Betz, Abdulhakem Y. Elezzabi
Place of PublicationBellingham, Washington
PublisherSPIE
Pages112781C-1-112781C-10
Number of pages10
ISBN (Electronic)9781510633209
ISBN (Print)9781510633193
DOIs
Publication statusPublished - 27 Feb 2020
EventUltrafast Phenomena and Nanophotonics XXIV 2020 - San Francisco, United States
Duration: 2 Feb 20204 Feb 2020

Publication series

NameProceedings of SPIE
PublisherSPIE
Volume11278
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X

Conference

ConferenceUltrafast Phenomena and Nanophotonics XXIV 2020
CountryUnited States
CitySan Francisco
Period2/02/204/02/20

Keywords

  • Coherent nonlinear spectroscopy
  • Exciton dynamics four-wave mixing micro-spectroscopy
  • Transition metal dichalcogenides

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