Room-temperature anomalous Hall effect in bulk-insulating topological insulators (Bi,Sb)₂Te₃ on thulium iron garnets

Chun-Chia Chen^1*, J. S. Wei¹, S. R. Yang¹, M. X. Guo¹, C. K. Cheng², S. W. Huang¹, K. Y. Lin², K. H. M. Chen¹, Y. T. Fanchiang², M. Hong², J. Kwo¹

¹Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
²Graduate Institute of Applied Physics and Department of Physics, National Taiwan University, Taipei, Taiwan

* Presenter:Chun-Chia Chen, email:chunchia0913@gmail.com

Ferromagnetic topological insulators (TIs) with broken time reversal symmetry (TRS) have attracted intense attention in recent years. Quantum anomalous Hall effect (QAHE) is one of the well-studied phenomena, which enables the dissipationless chiral transport in QAH states and displays high potential in the development of TI-based devices with low-power consumption. Although QAHE has been realized in magnetically doped TI systems, the QAH regime is still restricted below 2 K.¹ An alternative way to induce the magnetic order into TI films is to interface the TI films with magnetic insulators (MIs) and magnetize them via magnetic proximity effect (MPE). MPE could generate a more uniform magnetization at higher temperature than that of transition-metal doping, viable for practical application. In this work, we report the structural and electrical transport properties of high-quality (Bi,Sb)₂Te₃ thin films by molecular beam epitaxy on sapphire and thulium iron garnet (Tm₃Fe₅O₁₂, TmIG) strained thin films of perpendicular magnetic anisotropy (PMA). By adopting a low-temperature growth method that we developed earlier for Bi₂Se₃ films on TmIG,² we demonstrated significantly improved film growth as evidenced by streaky reflection high-energy electron diffraction patterns attained at the very first quintuple (Bi,Sb)₂Te₃ layer deposited on TmIG. The bulk-insulating nature of an ideal TI in the (Bi,Sb)₂Te₃ films was confirmed by both electric transport measurement and angle-resolved photoemission spectroscopy. Magneto-transport were conducted with anomalous Hall effect (AHE) at least up to 300K was successfully observed in our TI/MI hetero-structure. Our work has demonstrated the enhancement of the magnetization in TI via MPE, and thus promotes the prospect to realize QAHE at higher temperature and future applications of TI-based devices.

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2. C. C. Chen, K. H. M. Chen, Y. T. Fanchiang, C. C. Tseng, S. R. Yang, C. N. Wu, M. X. Guo, C. K. Cheng, C. T. Wu, M. Hong, J. Kwo, arXiv:1809.04513 (2018).

Keywords: topological insulator, thulium iron garnet, anomalous Hall effect, magnetic proximity effect