  We report magnetotransport measurements in the NbN/ magnetic topological
insulator MnBi2Te4 (MBT)/ NbN junction at low temperature. At 10 mK, the
nonlinear current-voltage characteristic of the junction shows a tunneling
behavior, indicating the existence of interfacial potential barriers within the
heterostructure. Under an out of plane perpendicular magnetic field, a
transition from negative to positive magnetoresistance (MR) is found when
increasing the bias voltage. A proximity-induced superconducting gap is
estimated to be 0.1meV by a pair of differential resistance dips. Moreover, the
induced gap is enhanced by gradually tuning the Fermi level toward the charge
neutral point by a back gate voltage, which is ascribed to the increased
transport contribution of the topological surface states in MBT. Intriguingly,
the induced gap exhibits an anomalous magnetic field assisted enhancement,
which may originate from the spin orbit coupling and magnetic order of MBT. Our
results reveal the interplay between magnetism and superconductivity in MBT,
paving the way for further studies on topological superconductivity and chiral
Majorana edge modes in quantum anomalous Hall insulator/superconductor hybrid
systems.
