Snoke D, Denev S, Liu Y, Pfeiffer L, West K
Department of Physics and Astronomy, University of Pittsburgh, 3941 O'Hara Street, Pennsylvania 15260, USA.
Nature. 2002 Aug 15;418(6899):754-7. doi: 10.1038/nature00940.
During the past ten years, coupled quantum wells have emerged as a promising system for experiments on Bose condensation of excitons, with numerous theoretical and experimental studies aimed at the demonstration of this effect. One of the issues driving these studies is the possibility of long-range coherent transport of excitons. Excitons in quantum wells typically diffuse only a few micrometres from the spot where they are generated by a laser pulse; their diffusion is limited by their lifetime (typically a few nanoseconds) and by scattering due to disorder in the well structure. Here we report photoluminescence measurements of InGaAs quantum wells and the observation of an effect by which luminescence from excitons appears hundreds of micrometres away from the laser excitation spot. This luminescence appears as a ring around the laser spot; almost none appears in the region between the laser spot and the ring. This implies that the excitons must travel in a dark state until they reach some critical distance, at which they collectively revert to luminescing states. It is unclear whether this effect is related to macroscopic coherence caused by Bose condensation of excitons.
在过去十年中，耦合量子阱已成为用于激子玻色凝聚实验的一个有前景的系统，有大量理论和实验研究旨在证明这种效应。推动这些研究的问题之一是激子长程相干输运的可能性。量子阱中的激子通常仅从激光脉冲产生它们的位置扩散几微米；它们的扩散受到其寿命（通常为几纳秒）以及阱结构中无序导致的散射的限制。在此我们报告了对InGaAs量子阱的光致发光测量，并观察到一种效应，即激子发出的光出现在距激光激发点数百微米远的地方。这种光以围绕激光点的环形出现；在激光点和环之间的区域几乎没有光出现。这意味着激子必须以暗态行进，直到它们到达某个临界距离，在该距离处它们集体恢复到发光态。目前尚不清楚这种效应是否与激子玻色凝聚引起的宏观相干性有关。
