拓扑半金属中的超快光电流研究

拓扑半金属是根据动量空间拓扑不变量来定义的一类区别于普通金属的新兴拓扑非平庸物态，在其体内和表面都具有独特的能带和自旋结构。这一类材料中由超短光脉冲激发引起的超快光电流研究目前还缺乏相关报道。本项目将对这一方向做详细探讨，希望利用该类材料的内部本征属性并辅以外部手段来实现对超快光电流及其太赫兹发射谱进行有效调控，相关的研究结果也会对发展新型超快光电器件和新型太赫兹发射源有重要意义。本项目将：（1）通过时域太赫兹发射谱对超快光电流进行研究，研究拓扑半金属独其特能带和自旋结构与超快光电流之间的关系。（2）利用时间分辨光谱研究超快光电流中的激发态电子自旋动力学，深刻理解光电流中的电子自旋极化弛豫和电子微观散射机制。

Topological semimetals, different from the normal metal, are emerging topologically nontrivial phases of matter defined by the topological invariant in the momentum space. They have unique energy band structures and spin structures in both their bulk and surface states. Although extensive research work have already been done on the topological semimetals, investigations of the ultrafast photocurrents in these novel materials generated by the femtosecond or picosecond optical pulses are still elusive. In this proposal, we will carry out the corresponding studies, which might enable us to realize the efficient control of ultrafast photocurrents and their associated terahertz emission in these materials using both the intrinsic and external means. The related results could eventually lead to develop new types of ultrafast optoelectronic devices and terahertz emitters in the coming future. Our research will be mainly focused on two aspects: (1) We will use the time-domain terahertz emission spectroscopy to obtain the ultrafast photocurrents, and further explore how the unique band and spin structures in the topological semimetals affect the ultrafast photocurrents and their associated terahertz emission. (2) We will use the time-resolved optical.spectroscopy to study the carrier and spin dynamics in the ultrafast photocurrents, which can help us to reveal the detail scattering mechanisms dominating the spin relaxation in the topological semimetals.