Song Justin C W, Levitov Leonid S
Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA.
J Phys Condens Matter. 2015 Apr 29;27(16):164201. doi: 10.1088/0953-8984/27/16/164201. Epub 2015 Apr 2.
Long lifetimes of hot carriers can lead to qualitatively new types of responses in materials. The magnitude and time scales for these responses reflect the mechanisms governing energy flows. We examine the microscopics of two processes which are key for energy transport, focusing on the unusual behavior arising due to graphene's unique combination of material properties. One is hot carrier generation in its photoexcitation dynamics, where hot carriers multiply through an Auger type carrier-carrier scattering cascade. The hot-carrier generation manifests itself through elevated electronic temperatures which can be accessed in a variety of ways, in particular optical conductivity measurements. Another process of high interest is electron-lattice cooling. We survey different cooling pathways and discuss the cooling bottleneck arising for the momentum-conserving electron-phonon scattering pathway. We show how this bottleneck can be relieved by higher-order collisions—supercollisions—and examine the variety of supercollision processes that can occur in graphene.
热载流子的长寿命会导致材料中出现性质全新的响应类型。这些响应的幅度和时间尺度反映了能量流动的控制机制。我们研究了对能量传输至关重要的两个过程的微观情况，重点关注由于石墨烯独特的材料特性组合而产生的异常行为。一个是其光激发动力学中的热载流子产生，其中热载流子通过俄歇型载流子 - 载流子散射级联进行倍增。热载流子的产生通过升高的电子温度表现出来，这可以通过多种方式实现，特别是通过光导率测量。另一个备受关注的过程是电子 - 晶格冷却。我们考察了不同的冷却途径，并讨论了动量守恒电子 - 声子散射途径中出现的冷却瓶颈。我们展示了如何通过高阶碰撞——超级碰撞来缓解这个瓶颈，并研究了石墨烯中可能发生的各种超级碰撞过程。
