Conventional topological states are defined on flat Euclidean spaces. With acoustic metamaterials, we recently generalize the experimental study on topological states to curved surfaces and fractals.

Observation of topological p-orbital disclination states in non-Euclidian acoustic metamaterials
Ying Chen, Yuhang Yin, Zhi-Kang Lin, Z. H. Zheng, Y. Liu, J. Li, Jian-Hua Jiang, and Huanyang Chen
Phys. Rev. Lett. 129, 154301 (2022) (editor's suggestion) Web link

Observation of fractal higher-order topological states in acoustic metamaterials
S. Zheng, X. Man, Z.-L. Kong, Zhi-Kang Lin, G. Duan, N. Chen, D. Yu, Jian-Hua Jiang and Baizhan Xia,
Science Bulletin 67, 2069-2075 (2022). Web link

Higher-order topological phase in an acoustic fractal lattice
Junkai Li, Qingyang Mo, Jian-Hua Jiang and Zhaoju Yang
Science Bulletin 67, 2040-2044 (2022). Web link
Congratulations Ze-Lin and Zhi-Kang!