Magnetically doped topological insulators enable the quantum anomalous Hall effect which provides quantized edge states for lossless charge transport applications as well as for potential qubits based on chiral Majorana fermions.
The magnetic gap at the Dirac point of topological insulators which hosts the chiral edge states has so far never been observed directly. Here, we use low temperature ARPES to reveal the magnetic gap of Mn-doped Bi2Te3 films which is present only below the Curie temperature of 10-12 K. We discuss the size of the gap which is 5 times larger than predicted by density functional theory. We show that this enhancement is due to a remarkable structure modification induced by Mn doping. Instead of a disordered impurity system, it forms an alternating sequence of septuple and quintuple layer blocks, with Mn in the center of the septuple layers. Mn-doped Bi Se forms a similar heterostructure, however, only a large, albeit nonmagnetic gap is formed. We explain both differences based on the higher spin-orbit interaction in Bi2Te3 and discuss them in the context of the nonmagnetic system of In-doped Bi2Se3.
 E. D. L. Rienks et al., Large magnetic gap at the Dirac point in a Mn-induced Bi2Te3 heterostructure, arXiv:1810.06238
 J. Sánchez-Barriga et al., Anomalous behavior of the electronic structure of (Bi1-xInx )2Se3 across the quantum phase transition from topological to trivial insulator, Phys. Rev. B 98, 235110 (2018)