Ultrafast spin‐to‐charge conversion at the surface of topological insulator thin films

• Main Authors: Wang, Xinbo, Cheng, Liang, Zhu, Dapeng, Wu, Yang, Chen, Mengji, Wang, Yi, Zhao, Daming, Boothroyd, Chris Brian, Lam, Yeng Ming, Zhu, Jian-Xin, Battiato, Marco, Song, Justin Chien Wen, Yang, Hyunsoo, Chia, Elbert Ee Min
• Other Authors: School of Materials Science & Engineering
• Format: Article
• Language: English
• Published: 2020
• Subjects: Science::Physics; Spin‐to‐charge Conversion; Spintronics
• Online Access: https://hdl.handle.net/10356/138563
• Institution: Nanyang Technological University

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, an all‐optical method is presented, which 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, a giant terahertz emission is observed in the heterostructure that originates from spin‐to‐charge conversion, in which the topological surface states play a crucial role. A 0.12 ps timescale is identified that sets a technological speed limit of spin‐to‐charge conversion processes in topological insulators. In addition, it is shown 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 optospintronic devices based on topological insulators at room temperature.