Observation of a phononic higher-order Weyl semimetal

• Published in: Nature materials Vol. 20; no. 6; pp. 794 - 799
• Main Authors: Luo, Li, Wang, Hai-Xiao, Lin, Zhi-Kang, Jiang, Bin, Wu, Ying, Li, Feng, Jiang, Jian-Hua
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.06.2021; Nature Publishing Group
• Subjects: 639/301/1019/1015; 639/301/119/2792/4128; Acoustics; Anomalies; Biomaterials; Chemistry and Materials Science; Condensed Matter Physics; Crystal structure; Crystallinity; Letter; Materials Science; Metalloids; Metamaterials; Nanotechnology; Optical and Electronic Materials; Physical sciences; Physics; Symmetry; Topology
• ISSN: 1476-1122; 1476-4660; 1476-4660
• DOI: 10.1038/s41563-021-00985-6

Weyl semimetals (WSMs) 1 exhibit phenomena such as Fermi arc surface states, pseudo-gauge fields and quantum anomalies that arise from topological band degeneracy in crystalline solids for electrons 1 and metamaterials for photons 2 and phonons 3 . Here we report a higher-order Weyl semimetal (HOWSM) in a phononic system that exhibits topologically protected boundary states in multiple dimensions. We created the physical realization of the HOWSM in a chiral phononic crystal with uniaxial screw symmetry. Using acoustic pump–probe spectroscopies, we observed coexisting chiral Fermi arc states on two-dimensional surfaces and dispersive hinge arc states on one-dimensional hinge boundaries. These topological boundary states link the projections of the Weyl points (WPs) in different dimensions and directions, and hence demonstrate the higher-order topological physics 4 – 8 in WSMs. Our study further establishes the fundamental connection between higher-order topology and Weyl physics in crystalline materials and should stimulate further work on other potential materials, such as higher-order topological nodal-line semimetals. Symmetry is utilized to realize a phononic higher-order Weyl semimetal.