Resonantly hybridised excitons in moiré superlattices in van der Waals heterostructures

Abstract

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. A profound consequence of using these 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. Its presence in graphene/hexagonal boron nitride (hBN) structures led to the observation of electronic minibands, whereas its effect enhanced by interlayer resonant conditions in twisted graphene bilayers culminated in the observation of the superconductor-insulator transition at magic twist angles. Here, we demonstrate that, in semiconducting heterostructures built of incommensurate MoSe2 and WS2 monolayers, excitonic bands can hybridise, resulting 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 hybridisation of intra- and interlayer excitons, which manifests itself through a pronounced exciton energy shift as a periodic function of the interlayer rotation angle. This occurs as hybridised excitons (hX) are formed by holes residing in MoSe2 bound to a twist-dependent superposition of electron states in the adjacent monolayers. For heterostructures with almost aligned pairs of monolayer crystals, resonant mixing of the electron states leads to pronounced effects of the heterostructure's geometrical moiré pattern on the hX dispersion and optical spectrum. Our findings underpin novel strategies for band-structure engineering in semiconductor devices based on van der Waals heterostructures.

43 pages, 14 figures, includes supplementary information

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• Theory of optical absorption by interlayer excitons in transition metal dichalcogenide heterobilayers
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Cited by in corpus (8)

• Composite super-moiré lattices in double aligned graphene heterostructures
• Giant Valley-Zeeman Splitting from Spin-Singlet and Spin-Triplet Interlayer Excitons in WSe2/MoSe2 Heterostructure
• Ultra-thin van der Waals crystals as semiconductor quantum wells
• High resolution imaging of reconstructed domains and moire patterns in functional van der Waals heterostructure devices
• Moiré lattice-induced formation and tuning of hybrid dipolar excitons in twisted WS${}_2$/MoSe${}_2$ heterobilayers
• Electrically controllable router of interlayer excitons
• Spatially mixed moiré excitons in two-dimensional van der Waals superlattices
• Highly tunable quantum light from moiré trapped excitons