TOPOLOGICAL MATTER: Experimental observation of Weyl points.
Lu, Ling 1, *; Wang, Zhiyu 2; Ye, Dexin 2; Ran, Lixin 2; Fu, Liang 1; Joannopoulos, John D. 1; Soljacic, Marin 1
[Report] Science. 349(6248):622-624, August 7, 2015.

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: The massless solutions to the Dirac equation are described by the so-called Weyl Hamiltonian. The Weyl equation requires a particle to have linear dispersion in all three dimensions while being doubly degenerate at a single momentum point. These Weyl points are topological monopoles of quantized Berry flux exhibiting numerous unusual properties. We performed angle-resolved microwave transmission measurements through a double-gyroid photonic crystal with inversion-breaking where Weyl points have been theoretically predicted to occur. The excited bulk states show two linear dispersion bands touching at four isolated points in the three-dimensional Brillouin zone, indicating the observation of Weyl points. This work paves the way to a variety of photonic topological phenomena in three dimensions.

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