Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore, 637371, Singapore.
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China.
Adv Mater. 2018 Dec;30(52):e1802356. doi: 10.1002/adma.201802356. Epub 2018 Oct 29.
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 Bi Se /ferromagnetic Co heterostructure, down to the sub-picosecond timescale. Compared to pure Bi Se 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 Bi Se 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.
强自旋轨道耦合导致自旋动量锁定的表面态的形成，赋予拓扑绝缘体卓越的自旋到电荷转换特性，尽管控制它的动力学仍然难以捉摸。在这里，提出了一种全光学方法，能够以前所未有的精度跟踪原型拓扑绝缘体 Bi Se/铁磁 Co 异质结构中自旋到电荷转换的超快动力学，达到亚皮秒时间尺度。与纯 Bi Se 或 Co 相比，在异质结构中观察到巨大的太赫兹发射，这源于自旋到电荷的转换，其中拓扑表面态起着关键作用。确定了 0.12 ps 的时间尺度，这为拓扑绝缘体中的自旋到电荷转换过程设定了技术速度限制。此外，还表明，正如表面态的性质所预期的那样，自旋到电荷的转换效率在 Bi Se 中与温度无关，为设计基于拓扑绝缘体的室温下新一代高速光自旋电子器件铺平了道路。
