Fractal hierarchy enables exponential scaling of topological boundary states

L Limin Song Z Zhichan Hu Z Ziteng Wang D Domenico Bongiovanni L Liqin Tang (Department of Pharmacy, The First Affiliated Hospital of University of Science and Technology of China (USTC), Laboratory of Precision and Intelligent Chemistry, Department of Polymer Science and Engineering, University of Science and Technology of China, Hefei 230026, Anhui Province, China) D Daohong Song R Roberto Morandotti J Jingjun Xu H Hrvoje Buljan Z Zhigang Chen