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Résumé |
Monolayers of semiconducting transition metal dichalcogenides are direct band gap semiconductors.
Because of the lack of inversion symetry and of the large spin orbit interaction, the spin and valley degrees of
freedom are strongly coupled and a particular valley exciton population can be initialized using circularly
polarized light excitation. As two dimensional materials, monolayers can be stacked on top of one another in
the form of van der waals heterostructures to create artifical hetero- or homo- bilayers. These artifical
structures can host different types of exciton complexes, in particular interlayer excitons for which electrons
and holes are in different layers. Recently, it was realized that the twist angle between the two layers can
strongly modify the electronic properties of the stack and can also be used to generate a lateral modulatin of
the potential through a Moiré pattern.
In this talk, I will describe interlayer excitons in homobilayers of 2H-MoS2 and present experimental evidence
for such excitons. In a second part, I will describe optical properties of a WSe2/MoSe2 heterobilayer in which
the two layers have been aligned with an angle close to 60∞ (2H stacking) to create a well defined band
structure together with a moiré potential. I will show how these particular structures, combined with the use
of high magnetic fields, allow for a rich spectroscopy of interlayer exciton scattering mechanisms. |
