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14 March 2016 Coherent quantum dynamics of excitons in monolayer transition metal dichalcogenides
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Transition metal dichalcogenides (TMDs) have garnered considerable interest in recent years owing to their layer thickness-dependent optoelectronic properties. In monolayer TMDs, the large carrier effective masses, strong quantum confinement, and reduced dielectric screening lead to pronounced exciton resonances with remarkably large binding energies and coupled spin and valley degrees of freedom (valley excitons). Coherent control of valley excitons for atomically thin optoelectronics and valleytronics requires understanding and quantifying sources of exciton decoherence. In this work, we reveal how exciton-exciton and exciton-phonon scattering influence the coherent quantum dynamics of valley excitons in monolayer TMDs, specifically tungsten diselenide (WSe2), using two-dimensional coherent spectroscopy. Excitation-density and temperature dependent measurements of the homogeneous linewidth (inversely proportional to the optical coherence time) reveal that exciton-exciton and exciton-phonon interactions are significantly stronger compared to quasi-2D quantum wells and 3D bulk materials. The residual homogeneous linewidth extrapolated to zero excitation density and temperature is ~1:6 meV (equivalent to a coherence time of 0.4 ps), which is limited only by the population recombination lifetime in this sample.
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Galan Moody, Kai Hao, Chandriker Kavir Dass, Akshay Singh, Lixiang Xu, Kha Tran, Chang-Hsiao Chen, Ming-Yang Li, Lain-Jong Li, Genevieve Clark, Gunnar Berghäuser, Ermin Malic, Andreas Knorr, Xiaodong Xu, and Xiaoqin Li "Coherent quantum dynamics of excitons in monolayer transition metal dichalcogenides", Proc. SPIE 9746, Ultrafast Phenomena and Nanophotonics XX, 97461T (14 March 2016);

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