  Breaking time reversal symmetry in a topological insulator may lead to
quantum anomalous Hall effect and axion insulator phase. MnBi4Te7 is a recently
discovered antiferromagnetic topological insulator with TN ~12.5 K, which is
constituted of alternatively stacked magnetic layer (MnBi2Te4) and non-magnetic
layer (Bi2Te3). By means of scanning tunneling spectroscopy, we clearly observe
the electronic state present at a step edge of a magnetic MnBi2Te4 layer but
absent at non-magnetic Bi2Te3 layers at 4.5 K. Furthermore, we find that as the
temperature rises above TN, the edge state vanishes, while the point defect
induced state persists upon temperature increasing. 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.
