Abstract
Topological photonics is rapidly expanding. However, discovering three-dimensional topological electromagnetic systems can be more challenging than electronic systems for two reasons. First, the vectorial nature of electromagnetic waves results in complicated band dispersions, and simple tight-binding-type predictions usually fail. Second, topological electromagnetic surface modes inside the light cone have very low quality factors (Q factors). Here, we propose the concept of scalar topological photonics to address these challenges. Our approach is experimentally validated by employing a nested meta-crystal configuration using connected coaxial waveguides. They exhibit scalar-wave-like band dispersions, making the search for photonic topological phases an easier task. Their surface states have skyrmion-like electric field distributions, resulting in a whole, bright surface state band inside the light cone continuum. As such, the topological surface states in our three-dimensional nested crystals can be exposed to air, making such systems well-suited for practical applications.
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Data availability
All data used in the analysis are available in Figshare with the identifier ‘https://doi.org/10.6084/m9.figshare.22736801’.
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Acknowledgements
This work is supported by the Hong Kong Research Grants Council (16310422, 16310420, 16307821 and AoE/P-502/20) and the Hong Kong Scholars Program (XJ2019007).
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B.Y. and C.T.C. conceived the idea; B.Y. and Q.G. designed the structure; B.Y., Q.G. and Z.Z. proposed the fabrication scheme; B.Y., Q.G. and D.W. carried out all measurements; B.Y., Q.G. and H.W. carried out all simulations; B.Y., Q.G., D.W., H.W., L.X., W.X., M.K., R.-Y.Z., Z.-Q.Z. and C.T.C. developed and carried out the theoretical analysis; and B.Y., Q.G., Z.Z. and C.T.C. supervised the whole project. B.Y. and Q.G. wrote the paper and the Supplementary Information with input from all other authors.
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Nature Materials thanks Jordi Gomis Bresco, Paloma Huidobro and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Supplementary Figs. 1–16 and Texts I–III.
Supplementary Video 1
A 3D metal printed conventional cell of the nested meta-crystal, where the core and cladding tube are separated.
Supplementary Video 2
The relative displacements between the core and cladding tube.
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Yang, B., Guo, Q., Wang, D. et al. Scalar topological photonic nested meta-crystals and skyrmion surface states in the light cone continuum. Nat. Mater. 22, 1203–1209 (2023). https://doi.org/10.1038/s41563-023-01587-0
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DOI: https://doi.org/10.1038/s41563-023-01587-0
