Topological rainbow trapping in gradient photonic structure for terahertz band Wenwen Wang, Yun Shen, Huichang Li and Xiaohua Deng Eur. Phys. J. D, 79 7 (2025) 88 Published online: 25 July 2025 DOI: 10.1140/epjd/s10053-025-01033-7