Design of Antiferromagnetic Second-Order Band Topology with Rotation Topological Invariants in Two Dimensions.

The existence of fractionally quantized topological corner charge serves as a key indicator for two-dimensional (2D) second-order topological insulators (SOTIs), yet it has not been experimentally observed in realistic materials. Here, based on effective model analysis and symmetry arguments, we propose a strategy for achieving SOTI phases with in-gap corner states in 2D systems with antiferromagnetic (AFM) order. We discover that the band topology originates from the interplay between intrinsic spin-orbital coupling and interlayer AFM exchange interactions. Using first-principles calculations, we show that the 2D AFM SOTI phase can be realized in (MnBi 2 Te 4 )(Bi 2 Te 3 ) m films. Moreover, we demonstrate that the SOTI states are linked to rotation topological invariants under 3-fold rotation symmetry C 3 , resulting in fractionally quantized corner charge, i.e., n 3 | e | (mod e ). Due to the great achievements in (MnBi 2 Te 4 )(Bi 2 Te 3 ) m systems, our results providing reliable material candidates for experimentally accessible AFM SOTIs should draw intense attention.