Nodal Rings and Drumhead Surface States in Phononic Crystals Nodal Rings and Drumhead Surface States in Phononic Crystals The authors are Deng Weiyin, Lu Jiuyang, Li Feng, Huang Xueqin, Yan Mou, Ma Jiahong, Liu Zhengyou. This paper reports the important progress of the artificial microstructure Materials and Devices team in the School of Physics and Optoelectronics of SOUTH China University of Technology on three-dimensional topological phononic crystals. Postdoctoral fellow Deng Weiyin, Associate Professor Lu Jiuyang and Professor Li Feng are the co-first authors of this paper.

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  Topological semi-metals are a new class of topological phases, which possess a non - trivial volume dispersion. Topological semi-metals can be divided into nodal semi-metals (such as Dirac and Weyl) and nodal semi-metals according to the distribution of band intersections in momentum space. In recent years, the realization and potential application of topological semi-metals in phononic crystals have attracted much attention. Previously, the same team observed the acoustic Weyl point and the corresponding Fermi arc surface states in phononic crystals for the first time, published in Nature Physics [Li Feng, Huang Xueqin, Lu Jiuyang, Ma Jiahong, Liu Zhengyou 14, 30 (2018)]. This time, the team successfully realized a phononic crystal with nodal line configuration, and clearly observed nodal line body dispersion and corresponding tympanic membrane surface states.

  In topological nodal semi-metals, the intersections of energy bands form continuous closed loops in momentum space. The team theoretically predicted and designed phononic crystal structures with nodal lines in which sound waves have circular nodal line dispersion (Figs. A and B). Topologically non-banal topological nodal phonons induce surface states with tympanic membrane dispersion on the sample surface. The team experimentally observed the tympanic membrane surface states and measured their dispersion (Figs. C and D), and further verified the anti-disturbance ability of surface states against disorder. These results provide an ideal platform for exploring novel acoustic topological transport phenomena.

Figures (a) and (b) : simulation and experiment of annular nodal line dispersion; (c) and (d) : simulation and experimental diagram of topological surface state tympanic membrane dispersion.

  Founded in 2015, the team is engaged in the research of artificial structure physics. Previously, the team has published papers in Nature Materials and Physical Review Letters and other internationally famous journals with the south China University of Technology as the first unit. Among them, Li Feng and Huang Xueqin were introduced by Outstanding Talents and Team Introduction Program of South China University of Technology, and Lu Jiuyang and Deng Weiyin were supported by Postdoctoral Innovative Talents Program. This research project is supported by the National Natural Science Foundation of China and the Pearl River Talents Program of Guangdong Province.