  Intrinsic magnetic topological insulators from MnBi2Te4 family promise
realization of axion insulator, a theoretically predicted state of matter
capable to mutually convert electric and magnetic signals, and whose properties
are reminiscent of cosmological axion dark matter. Here we report the first
experimental realization of room-temperature axionic single-spin switch in
topological metamaterial MnBi2Te3. The metamaterial was in situ created in the
scanning tunneling microscopy (STM) experiment by removing Te atomic layer from
MnBi2Te4 surface using STM tip. Room temperature STM study of MnBi2Te3 revealed
atomic scale variations of exchange gap and formation of nanoscale spin bubbles
pinned at subsurface defects. We found that individual spin states in MnBi2Te3
can be reversibly switched using local electric field of STM tip with
magnetoelectric response comparable to the theoretically predicted response of
axion insulator. The observed topological surface magnetism develops
significantly above bulk N\'eel temperature.
