Quantized Magnetoelectric Effect in antiferromagnetic MnBi₂Te₄ Tunnel Junctions

Intrinsic magnetic topological insulators such as layered MnBi₂Te₄ are believed to be axion insulators exhibiting exotic physical properties at low temperatures. However, direct identification of axion insulators remains experimentally elusive because the observed vanishing Hall resistance, while indicating the onset of the axion field, is insufficient to distinguish between an axion insulator and a trivial insulator. We conceive a tunnel junction with the barrier being an antiferromagnetic topological insulator and study its magnetoelectric responses arising from the axion field. Using time-dependent non-equilibrium Green's functions, we theoretically demonstrate that if the tunnel barrier is indeed an axion insulator, it should be directly reflected in the quantized tunnel current density. We benchmark our results against multiple material factors such as system size and concentration of impurities, confirming unambiguously the validity of our proposed setup in identifying axion insulators.