Plasmon-exciton coupling evolution by dynamic molecular aggregation

Introduction The coupling of localized surface plasmons and excitons in semiconductor materials is an extremely powerful strategy to mould the properties of metal nanoparticles and nanoemitters. In fact, when the coupling... [ view full abstract ]

Introduction

The coupling of localized surface plasmons and excitons in semiconductor materials is an extremely powerful strategy to mould the properties of metal nanoparticles and nanoemitters. In fact, when the coupling between the modes dominates over losses, the resulting modes are characterized by an hybrid wavefunction, corresponding to an effective mixture of light and matter components (namely, plasmon-exciton polaritons), thus offering unique possibilities to dress plasmons with excitonic nonlinearities. 

Strong coupling between excitons and plasmons has been extensively studied in gold, silver and aluminum nanostructures, either with individual or array of nanoparticles. In this work, by integrating plasmonic nanostructure arrays in a microfluidic device, we show the real time build-up of plasmon-exciton strong coupling, and follow its evolution from the uncoupled modes to the ultra-strong regime.

Results and discussion

By injecting a dilute solution of a near-infrared cyanine dye, we clearly observe the transition from a crossing to an anticrossing behaviour in the plasmon-exciton extinction dispersion, and an increase of the Rabi splitting due to the progressive deposition of injected molecules on the metallic nanostructures surface. In particular, for sufficiently long interaction times, the Rabi splitting increases up to the 35% of the exciton energy (around 600 meV), thus entering the regime of ultrastrong coupling. Our results can open the way towards a full active control of the Rabi splitting in plasmonic systems, spanning from the strong to the ultrastrong regime.