Emerging weak localization effects on a topological insulator-insulating ferromagnet (Bi2Se3-EuS) interface

Thin films of topological insulator Bi2Se3 were deposited directly on insulating ferromagnetic EuS. Unusual negative magnetoresistance was observed near the zero field below the Curie temperature T-C, resembling the weak localization effect; whereas the usual positive magnetoresistance was recovered above T-C. Such negative magnetoresistance was only observed for Bi2Se3 layers thinner than t similar to 4 nm, when its top and bottom surfaces are coupled. These results provide evidence for a proximity effect between a topological insulator and an insulating ferromagnet, laying the foundation for future realization of the half-integer quantized anomalous Hall effect in three-dimensional topological insulators.