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 [3]. 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 [5].
[1] G. Wang et al, PRL 114, 97403 (2015)
[2] G. Wang et al, Nature Com. 6, 10110 (2015)
[3] J. P. Echeverry, ArXiv 1601.07351 (2016)
[4] G. Wang et al, PRL 115, 117401 (2015)
[5] G. Wang et al, 2D Mat. 2, 34002 (2015)
|