Topological insulators (TIs) are a novel class of quantum materials characterized by an insulating bulk and metallic conducting states at the surface. This metallic behavior however, can be changed by applying a magnetic field or, equivalently, by coupling the TI to a ferromagnetic material. In this work, for the first time, MRSEC researchers have succeeded in turning the TI surface states into an insulating state by coupling the TI to a ferromagnetic insulator. Moreover, because the ferromagnetic insulator has magnetic domains, a novel type of conducting channel appears on the surface of the TI exactly at the domain boundary. These topological conducting states have long been theoretically proposed but only now observed. These results pave the way to the observation of many theoretically predicted novel properties specific to TIs, and may also lead to future device applications.
