Hybrid photonic-plasmonic cavities have emerged as a new platform to increase light–matter interaction capable to enhance the Purcell factor in a singular way not attainable with either photonic or plasmonic cavities separately. In the hybrid cavities proposed so far, the plasmonic element is usually a metallic bow-tie antenna, so the plasmonic gap—defined by lithography—is limited to minimum values of several nanometers. Nanoparticle-on-a-mirror (NPoM) cavities are far superior to achieve the smallest possible mode volumes, as plasmonic gaps smaller than 1 nm can be created. Here, we design a hybrid cavity that combines an NPoM plasmonic cavity and a dielectric-nanobeam photonic crystal cavity operating at transverse-magnetic polarization. The metallic nanoparticle can be placed very close ($<1\mathrm{nm}$) to the upper surface of the dielectric cavity, which acts as a low-reflectivity mirror. We demonstrate through numerical calculations of the local density of states that this hybrid plasmonic-photonic cavity exhibits quality factors $Q$ above ${10}^3$ and normalized mode volumes $V$ down to ${10}^{-3}$, thus resulting in high Purcell factors ($F_P\approx {10}^5$), while being experimentally feasible with current technology. Our results suggest that hybrid cavities with sub-nanometer gaps should open new avenues for boosting light–matter interaction in nanophotonic systems.

中文翻译：

---

基于纳米粒子镜面配置的混合光子 - 等离子体腔

混合光子-等离子体腔已成为一种新平台，可以增加光-物质相互作用，能够以单独的方式增强珀塞尔因子，这是光子腔或等离子体腔分别无法实现的。在迄今为止提出的混合腔中，等离子体元件通常是金属蝴蝶结天线，因此由光刻定义的等离子体间隙被限制在几个纳米的最小值。镜上纳米粒子 (NPoM) 腔远优于实现最小可能的模式体积，因为可以创建小于 1 nm 的等离子体间隙。在这里，我们设计了一个混合腔，它结合了 NPoM 等离子体腔和在横向磁极化下工作的介电纳米束光子晶体腔。金属纳米粒子可以放置得非常近（$<1\mathrm{纳米}$) 到电介质腔的上表面，作为低反射镜。我们通过局部状态密度的数值计算证明了这种混合等离子体-光子腔具有品质因素$问$ 以上 ${10}^3$ 和归一化模式体积 $伏$ 向下 ${10}^{-3}$，从而导致高珀塞尔因子（$F_{磷}\approx {10}^5$)，同时使用当前技术在实验上是可行的。我们的研究结果表明，具有亚纳米间隙的混合腔应该为促进纳米光子系统中的光-物质相互作用开辟新的途径。