  The quantum anomalous Hall effect (QAHE) is an exotic quantum phenomenon
originating from dissipation-less chiral channels at the sample edge. While the
QAHE has been observed in magnetically doped topological insulators (TIs),
exploiting magnetic proximity effect on the TI surface from adjacent
ferromagnet layers may provide an alternative approach to the QAHE by opening
an exchange gap with less disorder than that in the doped system. Nevertheless,
the engineering of a favorable heterointerface that realizes the QAHE based on
the magnetic proximity effect remains to be achieved. Here, we report on the
observation of the QAHE in a proximity coupled system of non-magnetic TI and
ferromagnetic insulator (FMI). We have designed sandwich heterostructures of
(Zn,Cr)Te/(Bi,Sb)2Te3/(Zn,Cr)Te that fulfills two prerequisites for the
emergence of the QAHE; the formation of a sizable exchange gap at the TI
surface state and the tuning of the Fermi energy into the exchange gap. The
efficient proximity coupling in the all-telluride based heterostructure as
demonstrated here will enable a realistic design of versatile tailor-made
topological materials coupled with ferromagnetism, ferroelectricity,
superconductivity, and so on.
