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 () and Andrea Alù ()
Additional contact information
Guangwei Hu: National University of Singapore
Qingdong Ou: Monash University
Guangyuan Si: Victorian Node of the Australian National Fabrication Facility
Yingjie Wu: Monash University
Jing Wu: Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research)
Zhigao Dai: Monash University
Alex Krasnok: City University of New York
Yarden Mazor: The University of Texas at Austin
Qing Zhang: National University of Singapore
Qiaoliang Bao: Monash University
Cheng-Wei Qiu: National University of Singapore
Andrea Alù: City University of New York

Nature, 2020, vol. 582, issue 7811, 209-213

Abstract: 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.

Date: 2020
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DOI: 10.1038/s41586-020-2359-9

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