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Title: Topological triply degenerate point with double Fermi arcs
Authors: Yang, Yihao
Sun, Hong-Xiang
Xia, Jian-Ping
Xue, Haoran
Gao, Zhen
Ge, Yong
Jia, Ding
Yuan, Shou-Qi
Chong, Yidong
Zhang, Baile
Keywords: Science::Physics
Issue Date: 2019
Source: Yang, Y., Sun, H.-X., Xia, J.-P., Xue, H., Gao, Z., Ge, Y., . . . Zhang, B. (2019). Topological triply degenerate point with double Fermi arcs. Nature Physics, 15(7), 645-649. doi:10.1038/s41567-019-0502-z
Journal: Nature Physics
Abstract: Unconventional chiral particles have recently been predicted to appear in certain three-dimensional crystal structures containing three- or more-fold linear band degeneracy points (BDPs)1,2,3,4. These BDPs carry topological charges, but are distinct from the standard twofold Weyl points or fourfold Dirac points, and cannot be described in terms of an emergent relativistic field theory1. Here we report on the experimental observation of a topological threefold BDP in a three-dimensional phononic crystal. Using direct acoustic field mapping, we demonstrate the existence of the threefold BDP in the bulk band structure, as well as doubled Fermi arcs of surface states consistent with a topological charge of 2. Another novel BDP, similar to a Dirac point but carrying non-zero topological charge, is connected to the threefold BDP via the doubled Fermi arcs. The Fermi arcs form double helicoids spanning a broad frequency range (relative bandwidth >25%). We show that the non-contractibility of these arcs gives rise to the phenomenon of topologically protected negative refraction of surface states on all surfaces of the sample. Our work paves the way to using these unconventional particles for exploring new emergent physical phenomena, and may find applications in symmetry-stabilized three-dimensional zero-index metamaterials.
ISSN: 1745-2473
DOI: 10.1038/s41567-019-0502-z
DOI (Related Dataset): 10.21979/N9/4G3YST
Schools: School of Physical and Mathematical Sciences 
Organisations: Centre for Disruptive Photonic Technologies
The Photonics Institute
Rights: © 2019 The Author(s), under exclusive licence to Springer Nature Limited. All rights reserved. This paper was published in Nature Physics and is made available with permission of The Author(s), under exclusive licence to Springer Nature Limited.
Fulltext Permission: open
Fulltext Availability: With Fulltext
Appears in Collections:SPMS Journal Articles

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