Hybrid photonic-plasmonic cavities based on the nanoparticle-on-a-mirror configuration

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DOI http://dx.doi.org/10.1364/PRJ.433761
Reference A.I. Barreda, M. Zapata-Herrera, I.M. Palstra, L. Mercadé, J. Aizpurua, A.F. Koenderink and A. Martínez, Hybrid photonic-plasmonic cavities based on the nanoparticle-on-a-mirror configuration, Photonics Res. 9, (12), 2398-2419 (2021)
Group Resonant Nanophotonics

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. Nanoparticleon-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 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 103 and normalized mode volumes V down to 10-3, thus resulting in high Purcell factors (F P ≈ 105), 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.