Giant ultrafast spin injection and spin-to-charge conversion in topological materials

Ee Min Chia^1*

¹Division of Physics and Applied Physics, Nanyang Technological University, Singapore, Singapore

* Presenter:Ee Min Chia, email:elbertchia@ntu.edu.sg

In this talk I will show terahertz (THz) emission data on spin-to-charge conversion processes in ferromagnet/topological material (TM) heterostructures, where the TM is the Bi2Se3 topological insulator or the monolayer 2D transition metal dichalcogenide MoS2, both of which possess large spin-orbit coupling. In Co/Bi2Se3, we observe a giant THz emission that is predominantly spin-mediated, 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 [1]. In Co/MoS2, by making use of the strongly out-of-equilibrium character of the injected spins, we demonstrate a highly-efficient spin injection from a ferromagnet into a semiconductor, thus overcoming the crippling problem of impedance mismatch. Astonishingly, we measure a giant spin current that is orders of magnitude larger than typical injected spin current densities using currently available techniques [2].

[1] "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, and Elbert E. M. Chia, Advanced Materials, DOI:10.1002/adma.201802356 (2018).

[2] "Far out-of-equilibrium spin populations trigger ginant spin injection into atomically thin MoS2", Liang Cheng, Xinbo Wang, Weifeng Yang, Jianwei Chai, Ming Yang, Mengji Chen, Yang Wu, Xiaoxuan Chen, Dongzhi Chi, Kuan Eng Johnson Goh, Jian-Xin Zhu, Handong Sun, Shijie Wang, Justin C. W. Song, Marco Battiato, Hyunsoo Yang, and Elbert E. M. Chia, Nature Physics, DOI:10.1038/s41567-018-0406-3 (2019).

Keywords: spin-to-charge conversion, spin injection, THz emission spectroscopy, 2D transition metal dichalcogenide, topological insulators