  Inducing magnetism into topological insulators is intriguing for utilizing
exotic phenomena such as the quantum anomalous Hall effect (QAHE) for
technological applications. While most studies have focused on doping magnetic
impurities to open a gap at the surface-state Dirac point, many undesirable
effects have been reported to appear in some cases that makes it difficult to
determine whether the gap opening is due to the time-reversal symmetry breaking
or not. Furthermore, the realization of the QAHE has been limited to low
temperatures. Here we have succeeded in generating a massive Dirac cone in a
MnBi2Se4 /Bi2Se3 heterostructure which was fabricated by self-assembling a
MnBi2Se4 layer on top of the Bi2Se3 surface as a result of the co-deposition of
Mn and Se. Our experimental results, supported by relativistic ab initio
calculations, demonstrate that the fabricated MnBi2Se4 /Bi2Se3 heterostructure
shows ferromagnetism up to room temperature and a clear Dirac-cone gap opening
of ~100 meV without any other significant changes in the rest of the band
structure. It can be considered as a result of the direct interaction of the
surface Dirac cone and the magnetic layer rather than a magnetic proximity
effect. This spontaneously formed self-assembled heterostructure with a massive
Dirac spectrum, characterized by a nontrivial Chern number C = -1, has a
potential to realize the QAHE at significantly higher temperatures than
reported up to now and can serve as a platform for developing future "
topotronics" devices.
