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 3d 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 3d electrons in the YIG film and delocalized electrons of the surface and bulk states in the Bi ₂ Se ₃ film.