Excitonic effects dominate the optical properties of 2D materials, and excitons have been observed both within a single layer, and between two layers of 2D materials. In 2023, a number of experiments on trilayer 2D structures uncovered new exciton states — quadrupolar and every-other-layer excitons — that have an electrically-tunable dipole moment and show a quantum many-body phase diagram.
Key advances
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In symmetric trilayer heterostructures such as WSe2/MoSe2/WSe2, WSe2/WS2/WSe2 and WS2/WSe2/WSe2, quadrupolar excitons with electrically tunable dipole moment and light–matter interaction have been observed.
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Quantum phase transitions between a repulsive quadrupolar triangular lattice and an attractive staggered dipolar IX square phase are revealed, as well as the emerging phase diagram of spontaneously ordered many-body exciton states.
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Optically bright every-other-layer dipolar exciton and its higher orbital state with a large electrical dipole twice that of IXs in TMD heterobilayers are observed in naturally 2H-stacked trilayer WSe2 and MoSe2.
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Quadrupolar and every-other-layer excitons integrate the high oscillator strength and giant electric dipole, representing an advantageous scenario for technological advances in photonics and optoelectronics.
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Acknowledgements
The author gratefully acknowledges the financial support by the National Science Foundation of China (NSFC) (grant no. 12274447), the National Key Research and Development Program (grant nos. 2023YFA1407000 and 2021YFA1202900).
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Du, L. New excitons in multilayer 2D materials. Nat Rev Phys 6, 157–159 (2024). https://doi.org/10.1038/s42254-024-00704-5
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DOI: https://doi.org/10.1038/s42254-024-00704-5
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