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Nature. 2019 Mar;567(7746):81-86. doi: 10.1038/s41586-019-0986-9. Epub 2019 Mar 6.

Resonantly hybridized excitons in moiré superlattices in van der Waals heterostructures.

Author information

1
Department of Physics and Astronomy, University of Sheffield, Sheffield, UK.
2
School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, UK.
3
National Graphene Institute, University of Manchester, Manchester, UK.
4
Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México, Ensenada, Mexico.
5
Department of Energy Engineering and Department of Chemistry, Ulsan National Institute of Science and Technology (UNIST), Ulsan, South Korea.
6
Department of Physics, Indian Institute of Technology Madras, Chennai, India.
7
Department of Engineering Science, University of Oxford, Oxford, UK.
8
Division of Physics and Semiconductor Science, Dongguk University-Seoul, Seoul, South Korea.
9
Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Warsaw, Poland.
10
National Institute for Materials Science, Tsukuba, Japan.
11
Henry Royce Institute for Advanced Materials, Manchester, UK.
12
School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, UK. vladimir.falko@manchester.ac.uk.
13
National Graphene Institute, University of Manchester, Manchester, UK. vladimir.falko@manchester.ac.uk.
14
Henry Royce Institute for Advanced Materials, Manchester, UK. vladimir.falko@manchester.ac.uk.
15
Department of Physics and Astronomy, University of Sheffield, Sheffield, UK. a.tartakovskii@sheffield.ac.uk.

Abstract

Atomically thin layers of two-dimensional materials can be assembled in vertical stacks that are held together by relatively weak van der Waals forces, enabling coupling between monolayer crystals with incommensurate lattices and arbitrary mutual rotation1,2. Consequently, an overarching periodicity emerges in the local atomic registry of the constituent crystal structures, which is known as a moiré superlattice3. In graphene/hexagonal boron nitride structures4, the presence of a moiré superlattice can lead to the observation of electronic minibands5-7, whereas in twisted graphene bilayers its effects are enhanced by interlayer resonant conditions, resulting in a superconductor-insulator transition at magic twist angles8. Here, using semiconducting heterostructures assembled from incommensurate molybdenum diselenide (MoSe2) and tungsten disulfide (WS2) monolayers, we demonstrate that excitonic bands can hybridize, resulting in a resonant enhancement of moiré superlattice effects. MoSe2 and WS2 were chosen for the near-degeneracy of their conduction-band edges, in order to promote the hybridization of intra- and interlayer excitons. Hybridization manifests through a pronounced exciton energy shift as a periodic function of the interlayer rotation angle, which occurs as hybridized excitons are formed by holes that reside in MoSe2 binding to a twist-dependent superposition of electron states in the adjacent monolayers. For heterostructures in which the monolayer pairs are nearly aligned, resonant mixing of the electron states leads to pronounced effects of the geometrical moiré pattern of the heterostructure on the dispersion and optical spectra of the hybridized excitons. Our findings underpin strategies for band-structure engineering in semiconductor devices based on van der Waals heterostructures9.

PMID:
30842637
DOI:
10.1038/s41586-019-0986-9

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