  The layered antiferromagnetic MnBi2Te4 films have been proposed to be an
intrinsic quantum anomalous Hall (QAH) insulator with a large gap. To realize
this proposal, it is crucial to open a magnetic gap of surface states. However,
recent experiments have observed gapless surface states, indicating the absence
of out-of-plane surface magnetism, and thus the quantized Hall resistance can
only be achieved at the magnetic field above 6 T. In this work, we propose to
induce out-of-plane surface magnetism of MnBi2Te4 films via the magnetic
proximity with magnetic insulator CrI3. Our calculations have revealed a strong
exchange bias ~ 40 meV, originating from the long Cr-eg orbital tails that
hybridize strongly with Te p-orbitals. By stabilizing surface magnetism, the
QAH effect can be realized in the MnBi2Te4/CrI3 heterostructure. Our
calculations also demonstrate the high Chern number QAH state can be achieved
by controlling external electric gates. Thus, the MnBi2Te4/CrI3 heterostructure
provides a promising platform to realize the electrically tunable zero-field
QAH effect.
