Strong coupling and catenary field enhancement in the hybrid plasmonic metamaterial cavity and TMDC monolayers

Researchers in the field of nanophotonics have spent significant time in recent years investigating fascinating concepts known as polaritons and/or plexcitons. These ideas revolve around the strong coupling of light photons and/or plasmons to excitons in semiconductor materials.

Excitons, or bound electron-hole pairs in semiconductors, collectively respond to external light fields. To improve the strong interaction between electromagnetic fields and matter, properly designed cavities such as metasurfaces, metagratings, and metamaterials containing quantum emitters (QEs) are required. For example, their resonance energies should be the same to evaluate the coupling strength between plasmons of metallic nanocavities and excitons in QEs.

As a result, significant coupling between resonantly matched metal surface plasmons and QE excitons results in the development of novel plasmon-exciton hybridized energy states known as excitons. Such significant coupling is possible when the energy exchange rates between these subsystems outpace the decay rates of the plasmon and exciton modes.

Plasmonic nanocavities are essential in plasmon-exciton strong coupling due to their tunability and ability to restrict electromagnetic fields in a compact volume. However, not all plasmonic nanostructures have the same tunability and field confinement properties. For example, single nanoparticles have reduced spatial confinement of electromagnetic fields and restricted tunability to match excitonic resonance. Furthermore, the exciton mode must be stable in order to realize and manage strong coupling for nanophotonic applications.

Researchers now report in Opto-Electronic Advances the successful development of strong plasmon-exciton coupling and catenary field enhancement in a hybrid plasmonic metamaterial cavity containing transition metal dichalcogenide (TMDC) monolayers.

Plasmonic metamaterial cavities were chosen for their capacity to restrict electromagnetic fields in an ultrasmall volume and their ease of integration with intricate structures.

The plasmon resonance of these cavities spans a wide frequency range, which may be adjusted by changing the size or thickness of the cavity gap. This tuning is consistent with the excitons of the WS₂, WSe₂, and MoSe₂ monolayers.

TMDC monolayers were chosen for their capacity to facilitate strong light-matter interactions due to their temperature stability, high radiative decay rate, and notable exciton binding energies. By combining these unique properties, a strong coupling regime was realized.

In addition, a concept of catenary-like field enhancement was developed to control coupling strength. It was discovered that the catenary field enhancement's strength decreases as the cavity's gap width rises, resulting in various levels of Rabi splitting.

Consequently, the predicted Rabi splitting in Au-MoSe₂ and Au-WSe₂ heterostructures ranged between 77.86 and 320 meV at ambient temperature. Increased cavity gap and thickness reduced the catenary field enhancement's strength and associated Rabi splitting.