The correlation of surface impurity states with the antiferromagnetic ground states is crucial for understanding the formation of the topological surface state in the antiferromagnetic topological insulators MnBi₂Te₄. By using low-temperature scanning tunneling microscopy and spectroscopy, we observed a localized bound state around the Mn-Bi antisite defect at the Te-terminated surface of the antiferromagnetic topological insulator MnBi₂Te₄. When applying a magnetic field perpendicular to the surface (B_z) from –1.5 to 3.0 T, the bound state shifts linearly to a lower energy with increasing B_z, which is attributed to the Zeeman effect. Remarkably, when applying a large range of B_z from –8.0 to 8.0 T, the magnetic field induced reorientation of surface magnetic moments results in an abrupt jump in the local density of states (LDOS), which is characterized by LDOS-change-ratio $\text{d}\tilde{\sigma }\text{/d}B$ quantitatively. Interestingly, two asymmetric critical field, –2.0 and 4.0 T determined by the two peaks in $\text{d}\tilde{\sigma }\text{/d}B$ are observed, which is consistent with simulated results according to a Mills-model, describing a surface spin flop transition (SSF). Our results provide a new flatform for studying the interplay between magnetic order and topological phases in magnetic topological materials.

The control of the Kondo effect is of great interest in single-molecule junction due to its potential applications in spin based electronics. Here, we demonstrate that the Kondo effect is reversibly switched on and off in an iron phthalocyanine (FePc) single-molecule junction by using a superconducting Nb tip. In a scanning tunneling microscope-based Nb-insulator-FePc-Au junction, we achieve a reversible switching between the Kondo dip and inelastic electronic tunneling spectra by simply adjusting the tip-sample distance to tune the tunnel coupling at low temperature. Further approaching the tip leads to the picking up of the molecule to the tip apex, which transfers the geometry of the single-molecule junction into a Nb-FePc-insulator-Au type. As the molecule forms an effective magnetic impurity embedded into the superconducting ground states of the Nb tip, the out-gap Kondo dip switched to an in-gap Yu–Shiba–Rusinov state. Our results open up a new route for manipulating the Kondo effect within a single-molecule junction.