Transition to strong coupling regime in hybrid plasmonic systems: exciton-induced transparency and Fano interference

Tigran V Shahbazyan

doi:10.1515/nanoph-2021-0246

Abstract

AbstractWe present a microscopic model describing the transition to a strong coupling regime for an emitter resonantly coupled to a surface plasmon in a metal–dielectric structure. We demonstrate that the shape of scattering spectra is determined by an interplay of two distinct mechanisms. First is the near-field coupling between the emitter and the plasmon mode which underpins energy exchange between the system components and gives rise to exciton-induced transparency minimum in scattering spectra prior to the transition to a strong coupling regime. The second mechanism is the Fano interference between the plasmon dipole and the plasmon-induced emitter’s dipole as the system interacts with the radiation field. We show that the Fano interference can strongly affect the overall shape of scattering spectra, leading to the inversion of spectral asymmetry that was recently reported in the experiment.

Highlights

Strong coupling between surface plasmons in metal– dielectric structures and excitons in semiconductors or dye molecules has recently attracted intense interest driven to a large extent by possible applications in ultrafast reversible switching [1,2,3], quantum computing [4, 5], and light harvesting [6]
We show that the Fano interference can strongly affect the overall shape of scattering spectra, leading to the inversion of spectral asymmetry that was recently reported in the experiment
We present a microscopic model for the linear optical response of a single exciton resonantly coupled to a surface plasmon mode in a metal–dielectric structure which accounts for both exciton-induced transparency (ExIT) and Fano interference effects as the system transitions to a strong coupling regime

Summary

Introduction

Strong coupling between surface plasmons in metal– dielectric structures and excitons in semiconductors or dye molecules has recently attracted intense interest driven to a large extent by possible applications in ultrafast reversible switching [1,2,3], quantum computing [4, 5], and light harvesting [6]. The scattering spectra of hybrid plasmonic systems, such as excitons in J-aggregates or colloidal QDs coupled to gap plasmons in nanoparticleon-metal systems [35,36,37,38] or those in two-dimensional atomic crystals conjugated with Ag or Au nanostructures [39,40,41,42,43,44], exhibit a narrow minimum even before reaching the strong coupling transition point The emergence of such a minimum in the weak coupling regime is referred to as exciton-induced transparency (ExIT) [45,46,47], in analogy to electromagnetically induced transparency (EIT) in pumped three-level atomic systems that is attributed to the Fano interference between different excitation pathways. We demonstrate that the Fano interference can lead to an inversion of spectral asymmetry, consistent with the experiment [22, 39, 40]

The system Hamiltonian and microscopic coupling parameters

Optical dipole moment of a hybrid plasmonic system

Numerical results and discussion

Conclusions