Koch S W, Kira M, Khitrova G, Gibbs H M
Department of Physics and Material Sciences Centre, Philipps-Universität, Renthof 5, D-35032 Marburg, Germany.
Nat Mater. 2006 Jul;5(7):523-31. doi: 10.1038/nmat1658.
Excitons are quasi-particles that form when Coulomb-interacting electrons and holes in semiconductors are bound into pair states. They have many features analogous to those of atomic hydrogen. Because of this, researchers are interested in exploring excitonic phenomena, from optical, quantum-optical and thermodynamic transitions to the possible condensation of excitons into a quantum-degenerate state. Excitonic signatures commonly appear in the optical absorption and emission of direct-gap semiconductor systems. However, the precise properties of incoherent exciton populations in such systems are difficult to determine and are the subject of intense debate. We review recent contributions to this discussion, and argue that to obtain detailed information about exciton populations, conventional experimental techniques should be supplemented by direct quasi-particle spectroscopy using the relatively newly available terahertz light sources. Finally, we propose a scheme of quantum-optical excitation to generate quantum-degenerate exciton states directly.
激子是一种准粒子，当半导体中通过库仑相互作用的电子和空穴束缚成配对状态时形成。它们具有许多与氢原子类似的特性。因此，研究人员对探索激子现象感兴趣，这些现象涵盖从光学、量子光学和热力学跃迁到激子可能凝聚成量子简并态等方面。激子特征通常出现在直接带隙半导体系统的光吸收和发射中。然而，此类系统中非相干激子群体的精确特性难以确定，并且是激烈争论的主题。我们回顾了近期对此讨论的贡献，并认为为了获得有关激子群体的详细信息，传统实验技术应辅以使用相对新出现的太赫兹光源的直接准粒子光谱学。最后，我们提出了一种量子光学激发方案，以直接产生量子简并激子态。
