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 Bi2Se3/ferromagnetic Co heterostructure, down to the sub-picosecond timescale. Compared to pure Bi2Se3 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 Bi2Se3 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.
@article{arxiv.1810.02253,
title = {Ultrafast Spin-To-Charge Conversion at the Surface of Topological Insulator Thin Films},
author = {Xinbo Wang and Liang Cheng and Dapeng Zhu and Yang Wu and Mengji Chen and Yi Wang and Daming Zhao and Chris B. Boothroyd and Yeng Ming Lam and Jian-Xin Zhu and Marco Battiato and Justin C. W. Song and Hyunsoo Yang and Elbert E. M. Chia},
journal= {arXiv preprint arXiv:1810.02253},
year = {2019}
}