发表机构
Institute of Experimental and Applied Physics, Kiel University; Faculty of Electrical and Computer Engineering, Tarbiat Modares University; Kiel Nano, Surface, and Interface Science KiNSIS, Kiel University（基尔大学实验与应用物理研究所; 塔比阿特·莫达雷斯大学电气与计算机工程学院; 基尔大学基尔纳米、表面与界面科学中心）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过阴极发光光谱发现电子束激发可增强层状半导体中激子极化激元的集体耦合强度，并揭示低能电子导致的非相干激发转变，为调控光-物质相互作用提供新途径。
AI 中文摘要
层状半导体中的自混合激子极化激元源于激子共振与薄膜中受限光子模式的杂化，为在纳米尺度控制光-物质相互作用提供了一个多功能平台。然而，激子-光子相互作用的本质以及多个激子与同一光子模式的集体同步强耦合在很大程度上仍未得到探索。在此，我们使用互补的动量分辨光致发光和阴极发光光谱，比较了Ruddlesden-Popper钙钛矿薄片在光学和电子束激发下的自混合激子极化激元。我们发现，阴极发光表现出比光致发光显著更大的极化激元能级排斥，揭示了电子束激发下增强的有效耦合强度。我们将这种增强归因于快电子对多个激子的集体相干激发，这些激子与同一光子模式耦合，并根据$g_N=g_1\sqrt{N}$标度增加相互作用强度，有效数量高达$N\approx23$个相干耦合的激子振荡器。通过降低电子动能，我们进一步揭示了一个向部分非相干激发区域的交叉，在该区域中，高阶法布里-珀罗激子极化激元共振消失，只留下最低的极化激元分支，而相干渡越辐射持续存在。这种转变是因为低能电子在扩展的空间体积上激发激子，冲刷掉了维持集体耦合和形成极化激元共振所需的相位相干性。我们的工作表明，电子束可以主动改变层状半导体中的集体光-物质耦合，并确立了阴极发光作为超越全光学激发方案的激发区域访问途径。
英文摘要
Self-hybridized exciton polaritons in layered semiconductors emerge from the hybridization of excitonic resonances with confined photonic modes in films and provide a versatile platform for controlling light--matter interactions at the nanoscale. Yet, the nature of exciton--photon interactions and the collective and synchronous strong coupling of multiple excitons to the same photonic mode remain largely unexplored. Here, we use complementary momentum-resolved photoluminescence and cathodoluminescence spectroscopy to compare self-hybridized exciton polaritons in Ruddlesden--Popper perovskite flakes under optical and electron-beam excitation. We find that cathodoluminescence exhibits remarkably larger polaritonic level repulsion than photoluminescence, revealing an enhanced effective coupling strength under electron-beam excitation. We attribute this enhancement to the collective coherent excitation of multiple excitons by fast electrons, which couple to the same photonic mode and increase the interaction strength according to a $g_N=g_1\sqrt{N}$ scaling, with an effective number of up to $N\approx23$ coherently coupled excitonic oscillators. By reducing the electron kinetic energy, we further uncover a crossover to a partially incoherent excitation regime in which higher-order Fabry--Pérot exciton-polariton resonances disappear, leaving only the lowest polariton branches while coherent transition radiation persists. This transition arises because low-energy electrons excite excitons over extended spatial volumes, washing out the phase coherence required to sustain collective coupling and form polaritonic resonances. Our work shows that electron beams can actively modify collective light--matter coupling in layered semiconductors and establishes cathodoluminescence as a route to access excitation regimes beyond all-optical excitation schemes.
