Time Reversal Symmetry Breaking in Topological Insulator/Magnetic Insulator Heterostructures Revealed by the Negative Magnetoresistance
S. R. Yang1*, K. H. M. Chen1, C. C. Chen1, C. N. Wu1, C. C. Tseng1, C. K. Cheng2, M. Hong2, J. Kwo1
1Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
2Department of Physics, National Taiwan University, Taipei, Taiwan
* Presenter:S. R. Yang
Topological insulator (TI) is a quantum material characterized by its nontrivial topology of the bulk state which leads to the emergence of topological surface states. Much efforts have been devoted to the breaking of time reversal symmetry (TRS) in TSSs to realize quantum anomalous Hall (QAH) state for dissipationless chiral edge transport. In this work, we show that TRS is broken by combining TI Bi2Se3 with the magnetic insulator yttrium iron garnet (YIG) through the magnetic proximity effect (MPE) that enables uniform magnetization without introducing crystal defects, as opposed to magnetic dopings of Cr into TI. We obtained high quality YIG thin films by sputtering followed by high temperature anneals, and Bi2Se3 thin films were deposited at 280°C on YIG film surface by MBE. As the temperature decreased, the distinctive negative magnetoresistance (MR) showed in Bi2Se3 heterostructures while MR in Bi2Se3 remain positive. Magnetoconductances can be well described by incorporating a weak localization term into the fitting function, which indicates the gap opening of TSSs according to the theory developed by Hai-Zhou et al1. The systematic dependence of the WL and WAL components on Bi2Se3 thickness varying from 7 to 40 nm will be reported. Our study may pave the way to raise the temperature at which QAH state is realized.

1. Hai-Zhou Lu, Junren Shi and Shun-Qing Shen, Phys. Rev. Lett. 107, 076801 (2011).

Keywords: Topological insulator, Magnetic insulator, Proximity effect