Scanning tunneling microscopy study of room-temperature functional behavior of intrinsic magnetic topological insulators

We present a scanning tunneling microscopy study of room-temperature topological surface states (TSS) on Bi-terminated MnBi₂Te₄. We found that Bi-termination has a larger exchange gap than Te-termination and a higher surface magnetic ordering temperature, making it a promising system for exploring axion electrodynamics. After compensating local surface charge carriers with an electric field of the tip, we observed nontrivial current plateaus and hysteresis loops on tunnel current-voltage characteristics, which we attributed to the compressibility phase transition of TSS and induction of axion insulator quantum dot (QD). Tunneling data allowed to determine the ratio of magnetic and electric fields in QD and estimate the Chern number of a current vortex as C∼10, which suggests the formation of collective rotational resonance. We found that magnetic defects inside QD can suppress rotational resonance, as manifested either in a halt of vortex rotation or the development of Schrödinger-cat-like superpositions of rotating and non-rotating states.