Detection of proximity-induced exchange gap of topological surface states in topological insulator-magnetic insulator heterostructures

Shang-Rong Yang¹, Yu-Ting Fanchiang^2*, Chun-Chia Chen¹, Chun-Chih Tseng¹, Yu-Chi Liu¹, Meng-Xin Guo¹, Minghwei Hong², Shang-Fan Lee³, Jueinai Kwo¹

¹Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
²Department of Physics, National Taiwan University, Taipei, Taiwan
³Institute of Physics, Academia Sinica, Taipei, Taiwan

* Presenter:Yu-Ting Fanchiang, email:ytfanchiang@gmail.com

Heterostructures of topological insulator (TI)/ferromagnetic insulator are promising for the development of next-generation dissipationless devices, where time-reversal symmetry (TRS) breaking of TI surfaces, and the resulting quantum phenomena such as quantum anomalous Hall effect (QAHE), may be stabilized by magnetic proximity effect (MPE) at a higher temperature. In this work, we report first detections of MPE-induced exchange gap of topological surface states in Bi₂Se₃/yttrium iron garnet and Bi₂Se₃/thulium iron garnet by magneto-transport measurements. The exchange gap suppresses the weak antilocalization effect, and further induces a weak localization manifested as negative magnetoresistance (MR). The magnitude of negative MR evolved with the tilted angles of applied fields, reflecting the variability of the gap size determined by the perpendicular magnetization. The TRS-breaking in Bi₂Se₃ is further evidenced by the observation of square anomalous Hall resistance loops which signify a long range ferromagnetic order, and anisotropic magnetoresistance. Taken together, our study provides a coherent picture of TRS-broken magneto-transport in TI/FI. The co-existing long-range ferromagnetic order and the exchange gap indicates that TI/FI is a suitable platform for further pursuing QAHE.

Keywords: topological insulator, magnetic insulator, interface, magneto-transport