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arXiv · 1810.02253

Ultrafast Spin-To-Charge Conversion at the Surface of Topological Insulator Thin Films

Xinbo Wang·Liang Cheng·Dapeng Zhu·Yang Wu·Mengji Chen·Yi Wang·Daming Zhao·Chris B. Boothroyd·Yeng Ming Lam·Jian-Xin Zhu·Marco Battiato·Justin C. W. Song·Hyunsoo Yang·Elbert E. M. Chia
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Abstract

Strong spin-orbit coupling, resulting in the formation of spin-momentum-locked surface states, endows topological insulators with superior spin-to-charge conversion characteristics, though the dynamics that govern it have remained elusive. Here, we present an all-optical method that enables unprecedented tracking of the ultrafast dynamics of spin-to-charge conversion in a prototypical topological insulator Bi$_2$Se$_3$/ferromagnetic Co heterostructure, down to the sub-picosecond timescale. Compared to pure Bi$_2$Se$_3$ or Co, we observe a giant terahertz emission in the heterostructure than originates from spin-to-charge conversion, in which the topological surface states play a crucial role. We identify a 0.12-picosecond timescale that sets a technological speed limit of spin-to-charge conversion processes in topological insulators. In addition, we show that the spin-to-charge conversion efficiency is temperature independent in Bi$_2$Se$_3$ as expected from the nature of the surface states, paving the way for designing next-generation high-speed opto-spintronic devices based on topological insulators at room temperature.

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Xinbo Wang, Liang Cheng, Dapeng Zhu, Yang Wu, Mengji Chen, Yi Wang, Daming Zhao, Chris B. Boothroyd, Yeng Ming Lam, Jian-Xin Zhu, Marco Battiato, Justin C. W. Song, Hyunsoo Yang, Elbert E. M. Chia. 2018-10-04. Ultrafast Spin-To-Charge Conversion at the Surface of Topological Insulator Thin Films. https://doi.org/10.1002/adma.201802356

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