Interface electronic structure at the topological insulator–ferrimagnetic insulator junction

An interface electron state at the junction between a three-dimensional topological insulator film, Bi 2 Se 3 , and a ferrimagnetic insulator film, Y 3 Fe 5 O 12 (YIG), was investigated by measurements of angle-resolved photoelectron spectroscopy and x-ray absorption magnetic circular dichroism. The surface state of the Bi 2 Se 3 film was directly observed and localized 3 d spin states of the Fe 3+ in the YIG film were confirmed. The proximity effect is likely described in terms of the exchange interaction between the localized Fe 3 d electrons in the YIG film and delocalized electrons of the surface and bulk states in the Bi 2 Se 3 film.