报告题目（Title）：二维半导体范德华异质结构的光学性质理论研究（Theoretical investigations of optical properties of 2D semiconductors in van der Waals heterostructures）
报告人（Speaker）：Iann Gerber （法国图卢兹大学）
The spectacular progress in controlling the electronic properties of graphene has triggered research in alternative atomically thin two-dimensional crystals. Monolayers (ML) of transitionmetal dichalcogenides (TMD) such as MoS2 have emerged as promising semiconductor nanostructures for optical and electronic applications, thanks to their unique exciton properties. In TMD monolayers, 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 of the absorbed or emitted photon can be directly associated with selective carrier excitation in one of the two non-equivalent K valleys. The spin and valley properties for both excitons and free carriers in TMD monolayers such as MoS2, MoSe2 and WSe2 can be investigated by optical spectroscopy  and supported by advanced ab initio scheme such as GW+BSE technique . In this talk I will review first the exciton and optical properties of TMD monolayers, the key role played by exciton exchange interaction will be discussed since it has a dramatic impact on both the luminescence yield through the interplay between bright and dark excitons [3,4]. Interestingly anisotropy effects in systems like ReS2, ReSe2 can be predicted too . In a second time, the building of van der Waals heterostructures will be presented and for instance the dielectric environment modifications induced by h-BN encapsulation will be shown . The homo-bilayer MoS2 system will be described in details, with a direct comparison between theoretical absorption spectra and reflectivity measurements, in which interlayer excitons can be created in some specific stacking configurations [7, 8]. Tuning interlayer exciton properties with electric field application will be discussed too .
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