thin films on thulium iron garnet heterostructures

Breaking time-reversal symmetry (TRS) in topological insulator (TI) leads to exotic phenomena such as quantum anomalous Hall effect (QAHE). The novel phenomena originated from a gap opening at the Dirac surface state by exchange interaction with magnetic elements. Magnetically doped TI was first reported to exhibit such an exchange gap, but the observation temperature of QAHE was less than 2 K. Another way to break TRS is through interfacial magnetic proximity effect (MPE) in TI/ferromagnetic insulator bilayer with a strong ferromagnetism and uniform interfacial magnetization. In this work, TI films Bi₂Se₃ were grown by molecular beam epitaxy on ferromagnetic thulium iron garnet (TmIG) with perpendicular magnetic anisotropy and high T_C above 500K. The band structures of 2-6 quintuple layer (QL) Bi₂Se₃/TmIG bilayers were investigated by angle-resolved photoemission spectroscopy. Comparative study in 2-6 QL Bi₂Se₃/sapphire was also performed. The energy gap opening at the surface state of Bi₂Se₃/TmIG is larger than that of Bi₂Se₃/sapphire by about 20 meV. The larger surface state gap of Bi₂Se₃/TmIG could be induced by MPE, on top of hybridization of top and bottom surfaces. Our study demonstrates the opportunity of probing interfacial band of TI-based heterostructures.