Strong coupling of localized plasmons and molecular excitons in nanostructured silver films

TL;DR

This paper demonstrates strong coupling between localized surface plasmons in nanostructured silver films and molecular excitons of Rhodamine 6G, resulting in hybrid polaritonic modes with significant Rabi splitting and enhanced Raman signals.

Contribution

It reports the experimental observation of tunable strong coupling and polariton formation in silver nanostructures with dye molecules, characterized by a large Rabi splitting of ~400 meV.

Findings

Giant Rabi-splitting energy of ~400 meV observed.

Surface-enhanced Raman scattering shows orders of magnitude increase.

Coupling strength scales with the square root of molecular density.

Abstract

We report on the resonant coupling between localized surface plasmon resonances (LSPRs) in nanostructured Ag films, and an adsorbed monolayer of Rhodamine 6G dye. Hybridization of the plasmons and molecular excitons creates new coupled polaritonic modes, which have been tuned by varying the LSPR wavelength. The resulting polariton dispersion curve shows an anticrossing behavior which is very well fit by a simple coupled-oscillator Hamiltonian, giving a giant Rabi-splitting energy of ~400 meV. The strength of this coupling is shown to be proportional to the square root of the molecular density. The Raman spectra of R6G on these films show an enhancement of many orders of magnitude due to surface enhanced scattering mechanisms; we find a maximum signal when a polariton mode lies in the middle of the Stokes shifted emission band.