Inducing an image magnetic monopole and Schrödinger cat states in a topological insulator at room temperature*

We present a scanning tunneling microscopy (STM) study of room temperature (RT) topological surface states (TSS) on Bi-terminated MnBi₂Te₄. We found that Bi-termination has a larger Dirac exchange gap than Te-termination and a higher surface magnetic ordering temperature, making it a promising system for exploring axion electrodynamics. After compensating for local surface charge carriers with an electric field of the STM tip, we observed nontrivial current plateaus and hysteresis loops on the tunnel current-voltage characteristics, which we attributed to the compressibility phase transition of TSS, i.e., the induction of an axion insulator quantum dot (QD) and image magnetic monopole. Analysis of tunneling data allowed us to determine the ratio of magnetic and electric fields in the QD and estimate the Chern number of a current vortex as C~10, which suggests the formation of a collective rotational resonance, a correlated many-body state exhibiting distant neighbor hopping. We found that magnetic defects located inside the QD can suppress rotational resonance, as manifested either in a halt of vortex rotation or the development of rational Schrödinger-cat-like superpositions of rotating and non-rotating states. STM experiment shows no wavefunction collapse.