Topological polaritons and photonic magic angles in twisted α-MoO3 bilayers

Guangwei Hu, Qingdong Ou, Guangyuan Si, Yingjie Wu, Jing Wu, Zhigao Dai, Alex Krasnok, Yarden Mazor, Qing Zhang, Qiaoliang Bao*, Cheng Wei Qiu*, Andrea Alù*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Twisted two-dimensional bilayer materials exhibit many exotic electronic phenomena. Manipulating the ‘twist angle’ between the two layers enables fine control of the electronic band structure, resulting in magic-angle flat-band superconductivity1,2, the formation of moiré excitons3–8 and interlayer magnetism9. However, there are limited demonstrations of such concepts for photons. Here we show how analogous principles, combined with extreme anisotropy, enable control and manipulation of the photonic dispersion of phonon polaritons in van der Waals bilayers. We experimentally observe tunable topological transitions from open (hyperbolic) to closed (elliptical) dispersion contours in bilayers of α-phase molybdenum trioxide (α-MoO3), arising when the rotation between the layers is at a photonic magic twist angle. These transitions are induced by polariton hybridization and are controlled by a topological quantity. At the transitions the bilayer dispersion flattens, exhibiting low-loss tunable polariton canalization and diffractionless propagation with a resolution of less than λ0/40, where λ0 is the free-space wavelength. Our findings extend twistronics10 and moiré physics to nanophotonics and polaritonics, with potential applications in nanoimaging, nanoscale light propagation, energy transfer and quantum physics.

Original languageEnglish
Pages (from-to)209-213
Number of pages5
JournalNature
Volume582
Issue number7811
DOIs
StatePublished - 11 Jun 2020
Externally publishedYes

Funding

FundersFunder number
ARC Centre of Excellence in Future Low-Energy Electronics Technologies
FLEET
National Science Foundation
U.S. Department of Defense
Office of Naval ResearchN00014-19-1-2011
Air Force Office of Scientific Research
Simons Foundation
Multidisciplinary University Research InitiativeFA9550-18-1-0379
Australian Research Council15270 00014, FT150100450, R-263-000-B91-305, IH150100006, CE170100039
Agency for Science, Technology and Research
National Natural Science Foundation of China51601131
Science and Engineering Research CouncilA1820g0087

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