Laboratoire de Physique des Solides, CNRS-UMR 8502, Université Paris-Sud, F-91405 Orsay, France.
Nano Lett. 2012 Jul 11;12(7):3532-6. doi: 10.1021/nl301035x. Epub 2012 Jun 5.
We discuss the ultrafast evolution of the surface electronic structure of the topological insulator Bi(2)Te(3) following a femtosecond laser excitation. Using time and angle-resolved photoelectron spectroscopy, we provide a direct real-time visualization of the transient carrier population of both the surface states and the bulk conduction band. We find that the thermalization of the surface states is initially determined by interband scattering from the bulk conduction band, lasting for about 0.5 ps; subsequently, few picoseconds are necessary for the Dirac cone nonequilibrium electrons to recover a Fermi-Dirac distribution, while their relaxation extends over more than 10 ps. The surface sensitivity of our measurements makes it possible to estimate the range of the bulk-surface interband scattering channel, indicating that the process is effective over a distance of 5 nm or less. This establishes a correlation between the nanoscale thickness of the bulk charge reservoir and the evolution of the ultrafast carrier dynamics in the surface Dirac cone.
我们讨论了拓扑绝缘体 Bi(2)Te(3) 的表面电子结构在飞秒激光激发后的超快演化。通过时间和角度分辨光电子能谱，我们直接实时可视化了表面态和体导带的瞬态载流子分布。我们发现，表面态的热化最初由来自体导带的带间散射决定，持续约 0.5 ps；随后，狄拉克锥非平衡电子需要几皮秒时间恢复费米-狄拉克分布，而它们的弛豫则持续超过 10 ps。我们测量的表面灵敏度使得能够估计体-表面带间散射通道的范围，表明该过程在 5nm 或更短的距离内有效。这在体电荷储层的纳米级厚度和表面狄拉克锥中超快载流子动力学的演化之间建立了相关性。
