Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA 19104, USA.
Proc Natl Acad Sci U S A. 2011 Jun 21;108(25):10050-5. doi: 10.1073/pnas.1102212108. Epub 2011 May 31.
Strong coupling of light with excitons in direct bandgap semiconductors leads to the formation of composite photonic-electronic quasi-particles (polaritons), in which energy oscillates coherently between the photonic and excitonic states with the vacuum Rabi frequency. The light-matter coherence is maintained until the oscillator dephases or the photon escapes. Exciton-polariton formation has enabled the observation of Bose-Einstein condensation in the solid-state, low-threshold polariton lasing and is also useful for terahertz and slow-light applications. However, maintaining coherence for higher carrier concentration and temperature applications still requires increased coupling strengths. Here, we report on size-tunable, exceptionally high exciton-polariton coupling strengths characterized by a vacuum Rabi splitting of up to 200 meV as well as a reduction in group velocity, in surface-passivated, self-assembled semiconductor nanowire cavities. These experiments represent systematic investigations on light-matter coupling in one-dimensional optical nanocavities, demonstrating the ability to engineer light-matter coupling strengths at the nanoscale, even in non-quantum-confined systems, to values much higher than in bulk.
在直接带隙半导体中，光与激子的强耦合导致了复合光子-电子准粒子（极化激元）的形成，其中能量在光子态和激子态之间以真空拉比频率相干地振荡。光物质的相干性一直保持到振荡器退相或光子逃逸。激子极化激元的形成使得在固态中观察到玻色-爱因斯坦凝聚、低阈值极化激元激射成为可能，并且对于太赫兹和慢光应用也很有用。然而，为了更高的载流子浓度和温度应用，仍然需要增加耦合强度。在这里，我们报告了尺寸可调的、异常高的激子极化激元耦合强度，其特征是真空拉比分裂高达 200 毫电子伏特，以及群速度的降低，这是在表面钝化的自组装半导体纳米线腔中实现的。这些实验代表了对一维光学纳米腔中光物质耦合的系统研究，证明了即使在非量子限制系统中，也能够在纳米尺度上工程化光物质耦合强度，使其达到比体相更高的值。
