In a class of crystalline materials in the noncentrosymmetric space group, the topological surface state in the whole Brillouin zone is a double helicoid.

From the article:

Double-Weyl Phonons in Transition-Metal Monosilicides
Tiantian Zhang, Zhida Song, A. Alexandradinata, Hongming Weng, Chen Fang, Ling Lu, and Zhong Fang
Phys. Rev. Lett. 120, 016401 (2018)

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