Observation of Magnetism-Induced Topological Edge State in Antiferromagnetic Topological Insulator MnBi 4 Te 7 .

Breaking time reversal symmetry in a topological insulator may lead to quantum anomalous Hall effect and axion insulator phase. MnBi 4 Te 7 is a recently discovered antiferromagnetic topological insulator with T N ∼ 12.5 K, which is composed of an alternatively stacked magnetic layer (MnBi 2 Te 4 ) and nonmagnetic layer (Bi 2 Te 3 ). By means of scanning tunneling spectroscopy, we clearly observe the electronic state present at a step edge of a magnetic MnBi 2 Te 4 layer but absent at nonmagnetic Bi 2 Te 3 layers at 4.5 K. Furthermore, we find that as the temperature rises above T N the edge state vanishes, while the point defect induced state persists upon an increase in temperature. These results confirm the observation of magnetism-induced edge states. Our analysis based on an axion insulator theory reveals that the nontrivial topological nature of the observed edge state.