Journal
NANO LETTERS
Volume 20, Issue 7, Pages 5323-5329Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.nanolett.0c01673
Keywords
Light canalization; Phonon Polaritons; van der Waals materials; s-SNOM; nano-optics; hyperbolic materials
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Funding
- Severo Ochoa Program from the Government of the Principality of Asturias [PA-18-PF-BP17-126, PA-20-PF-BP19-053]
- Ramo'n y Cajal Program from the Government of Spain [RYC2018-026196-I]
- Spanish Ministry of Science, Innovation and Universities [MAT2017-88358-C3-3-R]
- European Research Council [715496]
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Recent discoveries have shown that, when two layers of van der Waals (vdW) materials are superimposed with a relative twist angle between them, the electronic properties of the coupled system can be dramatically altered. Here, we demonstrate that a similar concept can be extended to the optics realm, particularly to propagating phonon polaritons-hybrid light-matter interactions. To do this, we fabricate stacks composed of two twisted slabs of a vdW crystal (alpha-MoO3) supporting anisotropic phonon polaritons (PhPs), and image the propagation of the latter when launched by localized sources. Our images reveal that, under a critical angle, the PhPs isofrequency curve undergoes a topological transition, in which the propagation of PhPs is strongly guided (canalization regime) along predetermined directions without geometric spreading. These results demonstrate a new degree of freedom (twist angle) for controlling the propagation of polaritons at the nanoscale with potential for nanoimaging, (bio)-sensing, or heat management.
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