Dresden 2020 – scientific programme
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DS: Fachverband Dünne Schichten
DS 11: 2D semiconductors and van der Waals heterostructures II (joint session HL/DS)
DS 11.1: Invited Talk
Monday, March 16, 2020, 15:00–15:30, POT 81
Resonantly hybridized excitons in moiré superlattices in van der Waals heterostructures — •Alexander Tartakovskii — Department of Physics and Astronomy, University of Sheffield, Sheffield, S3 7RH, UK
Recent years have seen significant effort in exploration of monolayer semiconductors such as transition metal dichalcogenides (TMDs) MoS2, WS2, MoSe2, WSe2 etc. Atomically-thin layers of two-dimensional materials can be assembled in vertical stacks held together by relatively weak van der Waals forces, allowing for coupling between monolayer crystals with incommensurate lattices and arbitrary mutual rotation. The lattice constant difference and the mutual rotation angle present new degrees of freedom for the design of novel meta-materials.
A profound consequence of using these new degrees of freedom is the emergence of an overarching periodicity in the local atomic registry of the constituent crystal structures, known as a moiré superlattice. Here, we show that in semiconducting heterostructures built of incommensurate MoSe2 and WS2 monolayers, excitonic bands can hybridize, which results in the resonant enhancement of the moiré superlattice effects. MoSe2 and WS2 are specifically chosen for the near degeneracy of their conduction band edges to promote the hybridization of intra- and interlayer excitons. For MoSe2/WS2 heterostructures with almost aligned pairs of monolayer crystals, the resonant mixing of the electron states leads to amplified effects of the heterostructure’s geometrical moiré pattern on the dispersion of the hybridised excitons.