Proximity-induced superconducting gap in the intrinsic magnetic topological insulator MnBi2Te4

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 Aind is estimated to be ???0.1 meV 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.