通过飞秒激光激发固体材料，可利用材料中不同自由度的响应时间尺度研究多体相互作用、追踪超快相变过程、实现光诱导新物态或隐藏态等，是凝聚态物理研究的前沿和重要探索方向。时间分辨角分辨光电子能谱是近十多年发展起来的研究量子材料在飞秒激光激发后超快电子结构动力学的关键实验手段。本文回顾了基于非线性光学晶体和高阶倍频的时间分辨角分辨光电子能谱的基本原理和组成，以及利用其对量子材料的超快电子结构动力学进行的研究。主要包括四个方面的研究进展：（1）量子材料的非占据电子态探测；（2）光诱导的超快电子结构相变；（3）关联电子材料中电声相互作用强度确定；（4）光致新物态。最后，讨论了时间分辨角分辨光电子能谱未来可能的发展方向。 

高性能时间分辨角分辨光电子能谱在量子材料中研究进展

多尺度研究铜/金刚石界面电子及热传输特性

The ultrafast dynamics of photoexcited carriers and coherent phonons in ultrathin Bi2Te3 thermoelectric films are studied through transient differential transmission spectroscopy. An ultralow frequency coherent optical phonon at 0.16 THz emerges, especially in ultrathin films, and it is ascribed to interlayer breathing modes. It can divide the ultrathin films into two groups which have out-of-phase vibration along the normal of a film plane, causing a destructive interference between in-plane propagating thermal waves in the two groups of quintuple layers, and thus possibly reducing the thermal conductivity of the ultrathin films. The excitation power dependence of ultrafast dynamics reveals carrier-carrier scattering dominating thermalization, which provides a microscopic understanding of the reported high electrical conductivity and anomalously high power factor of ultrathin Bi2Te3 films at room temperature.

Guowei Yang

Papers

Ultrafast dynamics of photoexcited carriers and coherent phonons in ultrathin Bi2Te3 thermoelectric films