Higher-Order Topological Phase in Twisted Bilayer Graphene

We propose the twisted bilayer graphenes with large angles as higher-order topological insulators, hosting topological corner charges. At large commensurate angles, the intervalley scattering opens up the bulk gap and the corner states occur at half filling. Based on both first-principles calculations and analytic analysis, we show the striking results that the emergence of the corner states does not depend on the choice of the specific angles as long as the underlying symmetries are intact [1]. Finally, using a photonic crystal platform, we show that the strong coupling regime in a moiré superlattice can realize cascades of stable topological flat bands at large twist angles [2]. 

Reference 

[1] Moon Jip Park, Youngkuk Kim, Gil Young Cho, and SungBin Lee Phys. Rev. Lett. 123, 216803 (2019)

[2] Chang-Hwan Yi, Hee Chul Park, Moon Jip Park Light: Science & Applications 11, 289 (2022)