Strong Coupling in a Hybrid System of Silver Nanoparticles and J-Aggregates at Room Temperature

A large Rabi splitting (170 meV) is demonstrated in a plasmonic nanocavity at room temperature. The nanocavity is a nanoparticle-on-mirror (NPoM) structure, which is composed of individual silver nanocube and silver film with a methylene blue (MB) monolayer spacer. Mode splitting is clearly observed from the dark-field measurements, which is due to strong coupling between plasmonic mode and excitonic mode. The cavity exhibits Q factors up to 13.2 and splitting-to-damping ratios are 1.2. The influences of MB concentration and sizes of nanoparticle on the coupling behaviors are scrutinized. A similar manner is found in both 75 nm silver-composed and 100 nm silver-composed cavity, and the threshold of MB concentration is 1.5 x 10-6 mol/L. In addition, we argue that when the size of nanoparticle increases, the coupling strength g will decrease. These results could open a new avenue toward not only in the field of controllable coupling integrated optical devices at room temperature but also the physical theory based on exciton-plasmon coupling.