Observation of Topological Edge States in Thermal Diffusion

• Published in: Advanced materials (Weinheim) 2022-08, Vol.34 (31), p.e2202257-n/a
• Main Authors: Hu, Hao, Han, Song, Yang, Yihao, Liu, Dongjue, Xue, Haoran, Liu, Gui‐Geng, Cheng, Zheyu, Wang, Qi Jie, Zhang, Shuang, Zhang, Baile, Luo, Yu
• Format: Article
• Language: English
• Subjects: Acoustic waves; Band theory; Decay rate; Diffusion rate; Eigenvalues; Thermal diffusion; thermal functional materials; Topological insulators; Topology
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.202202257

Topological band theory predicts that bulk materials with nontrivial topological phases support topological edge states. This phenomenon is universal for various wave systems and is widely observed for electromagnetic and acoustic waves. Here, the notion of band topology is extended from wave to diffusion dynamics. Unlike wave systems that are usually Hermitian, diffusion systems are anti‐Hermitian with purely imaginary eigenvalues corresponding to decay rates. By direct probe of the temperature diffusion, the Hamiltonian of a thermal lattice is experimentally retrieved, and the emergence of topological edge decays is observed within the gap of bulk decays. The results of this work show that such edge states exhibit robust decay rates, which are topologically protected against disorder. This work constitutes a thermal analogue of topological insulators and paves the way to exploring defect‐immune heat dissipation. Topological phases have been demonstrated in various wave systems, however, they still remain unexplored in a purely diffusive system. This work reveals the topological phase in a purely diffusive system, that is, a thermal lattice. The experimental results show that the nontrivial topological phase of the thermal lattice can enable thermal edge states that exponentially decay within the gap of bulk decays.