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Transverse photon spin of bulk electromagnetic waves in bianisotropic media


Photons possess spin degree of freedom, which plays an important role in various applications such as optical communications, information processing and sensing. In isotropic media, photon spin is aligned with the propagation direction of light, obeying the principle of spin momentum locking. Interestingly, surface waves decaying away from an interface have a photon spin transverse to its propagation, opening exciting opportunities for the observation of spin-dependent excitation in confined systems. Here, we propose and realize transverse photon spin (T-spin) in a bulk medium, without relying on the presence of any interfaces. We show the mapping of the T-spin of surface modes to that of the bulk modes by introducing bianisotropy into the medium. We further discover that the interface between two bianisotropic media of opposite orientations supports edge-dependent propagating modes with tunable cutoff frequencies. Our results provide a new platform for manipulating the spin–orbit interaction of electromagnetic waves.

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Fig. 1: T-spins in the bulk mode of a homogeneous medium.
Fig. 2: Demonstration of T-spin in a homogeneous metamaterial.
Fig. 3: Spin locked scattering from a finite-sized bianisotropic metamaterial.
Fig. 4: Interface modes and their propagation characteristics.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.


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This work is financially supported by the National Natural Science Foundation of China (NNSFC) under grants 61875051, 61625502, 61801426, 61574127 and 61372022 and the Top-Notch Young Talents Program of China. S.Z. acknowledges support from an ERC Consolidator Grant (TOPOLOGICAL), the Royal Society and the Wolfson Foundation and Horizon 2020 Action, projects 734578 (D-SPA) and 777714 (NOCTORNO).

Author information




L.P. conceived the idea. L.P. and S.Z. proposed the physical concept, formulated the theory and planned the experiments. L.P., L.D., K.W. and L.Z. conducted the experiments. F.G., G.W., Y.Y. and H.C. participated in the data processing and analysis. L.P., S.Z., F.G. and H.C. discussed the results and wrote the manuscript.

Corresponding authors

Correspondence to Liang Peng or Hongsheng Chen or Shuang Zhang.

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The authors declare no competing interests.

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Supplementary information

Supplementary Information

Supplementary details, discussion, derivations and Figs. 1–11.

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Peng, L., Duan, L., Wang, K. et al. Transverse photon spin of bulk electromagnetic waves in bianisotropic media. Nat. Photonics 13, 878–882 (2019).

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