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Article Dans Une Revue Nano Letters Année : 2016

Radiatively limited dephasing and exciton dynamics in MoSe2 monolayers revealed with four-wave mixing microscopy

Résumé

By implementing four-wave mixing micro-spectroscopy we measure coherence and population dynamics of the exciton transitions in monolayers of MoSe2. We reveal their dephasing times T2 and radiative lifetime T1 in a sub-picosecond (ps) range, approaching T2 =2T1 , and thus indicating radiatively limited dephasing at a temperature of 6 K. We elucidate the dephasing mechanisms by varying the temperature and by probing various locations on the flake exhibiting a different local disorder. At nano-second range, we observe the residual FWM produced by the incoherent excitons, which initially disperse towards the dark states, but then relax back to the optically active states within the light cone. By introducing polarization-resolved excitation, we infer inter-valley exciton dynamics, revealing an initial polarization degree of around 30%, constant during the initial sub-picosecond decay, followed by the depolarization on a picosecond timescale. The FWM hyperspectral imaging reveals the doped and undoped areas of the sample, allowing to investigate the neutral exciton, the charged one or both transitions at the same time. In the latter, we observe the exciton-trion beating in the coherence evolution indicating their coherent coupling.
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hal-01357636 , version 1 (01-09-2016)

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Tomasz Jakubczyk, Valentin Delmonte, Maciej Koperski, Karol Nogajewski, Clément Faugeras, et al.. Radiatively limited dephasing and exciton dynamics in MoSe2 monolayers revealed with four-wave mixing microscopy. Nano Letters, 2016, 16 (9), pp.5333-5339. ⟨10.1021/acs.nanolett.6b01060⟩. ⟨hal-01357636⟩
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