The spectacular progress in controlling the electronic properties of graphene has triggered research in alternative atomically thin two-dimensional crystals. Monolayers (ML) of transition-metal dichalcogenides such as MoS2 have emerged as very promising nanostructures for optical and spintronics applications. Inversion symmetry breaking together with the large spin-orbit interaction leads to a coupling of carrier spin and k-space valley physics, i.e., the circular polarization (σ+ or σ−) of the absorbed or emitted photon can be directly associated with selective carrier excitation in one of the two nonequivalent K valleys (K+ or K−, respectively).
We have investigated the spin and valley properties for both neutral and charged excitons in transition metal dichalcogenide monolayer MoS2, MoSe2 and WSe2 with cw and time-resolved polarized photoluminescence spectroscopy [1,2]. The key role played by exciton exchange interaction will be presented . We also demonstrate that the optical alignment of excitons (“exciton valley coherence”) can be achieved following one or two photon excitation [1,4].
Finally recent results on magneto-photoluminescence spectroscopy on MoSe2 and WSe2 in Faraday configuration up to 9 T will be presented; the results will be discussed in the framework of a k.p theory .
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 G. Wang et al, Nature Com. 6, 10110 (2015)
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Cedric Robert, Gang Wang, Fabian Cadiz, Andréa Balocchi, Mikhail M. Glazov, Thierry Amand, Iann Gerber, Delphine Lagarde, Bernhard Urbaszek, and Xavier Marie, "Spin and valley polarization in MoS2, MoSe2, and WSe2 monolayers
(Conference Presentation)," Proc. SPIE 9931, Spintronics IX, 99313C (Presented at SPIE Nanoscience + Engineering: August 31, 2016; Published: 4 November 2016); https://doi.org/10.1117/12.2237774.5167075285001.
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Study of self-shadowing effect as a simple means to realize nanostructured thin films and layers with special attentions to birefringent obliquely deposited thin films and photo-luminescent porous silicon