  Topological insulators (TIs) are emergent materials with unique band
structure, which allow the study of quantum effect in solids, as well as
contribute to high performance quantum devices. To achieve the better
performance of TI, here we present a co-doping strategy using synergistic
rare-earth Sm and transition-metal Fe dopants in Bi2Se3 single crystals, which
combine the advantages of both transition metal doped TI (high ferromagnetic
ordering temperature and observed QAHE), and rare-earth doped TI (large
magnetic moments and significant spin orbit coupling). In the as-grown single
crystals, clear evidences of ferromagnetic ordering were observed. The angle
resolve photoemission spectroscopy indicate the ferromagnetism opens a 44 meV
band gap at surface Dirac point. Moreover, the carrier mobility at 3 K is ~
7400 cm2/Vs, and we thus observed an ultra-strong Shubnikov-de Haas oscillation
in the longitudinal resistivity, as well as the Hall steps in transverse
resistivity below 14 T. Our transport and angular resolved photoemission
spectroscopy results suggest that the rare-earth and transition metal co-doping
in Bi2Se3 system is a promising avenue implement the quantum anomalous Hall
effect, as well as harnessing the massive Dirac fermion in electrical devices.
