论文标题
3D拓扑绝缘子表面状态下光电流的超快动力学
Ultrafast dynamics of photocurrents in surface states of 3D topological insulators
论文作者
论文摘要
本文回顾了有关使用时间和角度分辨的两光子光发射（2PPE）观察到的三维（3D）拓扑绝缘子（TIS）的拓扑表面状态（TSS）中超快电子动力学的实验工作。重点放在超快光电流的产生以及对其衰减的时间分辨观察中。 2PPE不仅允许将光电流与自旋偏振电子表面状态联系起来。探测携带电流的电子的不对称动量分布，可以研究控制时间域中异常电子传输的显微镜散射过程。 Ultrashort中红外泵脉冲不仅允许在SB $ _2 $ TE $ _3 $中对TSS的直接光学激发，而且还导致TSS人口在动量空间中的强烈不对称。 TSS的二维带映射表明，这种不对称性实际上代表了宏观光电，而发现光电流的螺旋依赖性很小。光电流衰减的时间分辨观察发现TSS中电子的平均自由路径巨大。
This article reviews experimental work on the ultrafast electron dynamics in the topological surface state (TSS) of three-dimensional (3D) topological insulators (TIs) observed with time- and angle-resolved two-photon photoemission (2PPE). The focus is laid on the generation of ultrafast photocurrents and the time-resolved observation of their decay. 2PPE not only allow to unambiguously relate the photocurrents to the spin-polarized electronic surface states. Probing of the asymmetric momentum distribution of the electrons carrying the current makes it possible to study the microscopic scattering processes that governs the unusual electron transport in the time domain. Ultrashort mid-infrared pump pulses permit not only a direct optical excitation of the TSS in Sb$_2$Te$_3$ but also lead to a strong asymmetry of the TSS population in momentum space. Two-dimensional band mapping of the TSS shows that this asymmetry is in fact representative for a macroscopic photocurrent while the helicity-dependence of the photocurrent is found to be small. The time-resolved observation of the photocurrent decay reveals a huge mean free path of the electrons in the TSS.
