Strongly Surface State Carrier-Dependent Spin-Orbit Torque in Magnetic Topological Insulators

Xiaoyu Che; Quanjun Pan; Božo Vareskic; Jingyi Zou; Lei Pan; Peng Zhang; Gen Yin; Hao Wu; Qiming Shao; Peng Deng; Kang L Wang

doi:10.1002/adma.201907661

Strongly Surface State Carrier-Dependent Spin-Orbit Torque in Magnetic Topological Insulators

Adv Mater. 2020 Apr;32(16):e1907661. doi: 10.1002/adma.201907661. Epub 2020 Feb 28.

Authors

Xiaoyu Che¹, Quanjun Pan¹, Božo Vareskic¹, Jingyi Zou¹, Lei Pan¹, Peng Zhang¹, Gen Yin¹, Hao Wu¹, Qiming Shao^{1

2}, Peng Deng¹, Kang L Wang¹

Affiliations

¹ Department of Electrical and Computer Engineering, Department of Physics and Astronomy and Department of Materials Science and Engineering, University of California, Los Angeles, CA, 90095, USA.
² Department of Electronic and Computer Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, 999077, China.

PMID: 32108391
DOI: 10.1002/adma.201907661

Abstract

The topological surface states (TSS) in topological insulators (TIs) can exert strong spin-orbit torque (SOT) on adjacent magnetization, offering great potential in implementing energy-efficient magnetic memory devices. However, there are large discrepancies among the reported spin Hall angle values in TIs, and its temperature dependence still remains elusive. Here, the spin Hall angle in a modulation-doped Cr-Bi_x Sb_2- _x Te₃ (Cr-BST) film is quantitatively determined via both transport and optic approaches, where consistent results are obtained. A large spin Hall angle of ≈90 in the modulation-doped Cr-BST film is demonstrated at 2.5 K, and the spin Hall angle drastically decreases to 0.3-0.5 as the temperature increases. Moreover, by tuning the top TSS carrier concentration, a competition between the top and bottom TSS in contributing to SOT is observed. The above phenomena can account for the large discrepancies among the previously reported spin Hall angle values and reveal the unique role of TSS in generating SOT.

Keywords: magneto-optic Kerr effect; magneto-transport; spin-orbit torque; topological insulators; topological surface states.

Abstract

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