Accessing the Exceptional Points in a Graphene Plasmon-Vibrational Mode Coupled System

The coupling of plasmons and vibrational modes has been routinely observed in graphene and other 2D systems in both near-field and far-field spectroscopy. However, the relation between coupling strength and modal losses, and exceptional point physics has not been discussed. Here we apply a non-Hermitian framework to a model system of molecular layers on graphene and show that the transition point between strong and weak coupling regimes coincides with the exceptional point of non-Hermitian physics. We further show that the exceptional point can be conveniently located by changing the incident angle of the light and the graphene Fermi energy. Finally, we show that enhanced spectral sensitivity is obtained from small changes in molecular film thickness when the system is tuned to the exceptional point.

Automated summary

In this study, the coupling of plasmons and vibrational modes in a model system of molecular layers on graphene was investigated using a non-Hermitian framework. It was found that the transition point between strong and weak coupling regimes coincides with the exceptional point of non-Hermitian physics. By changing the incident angle of light and the graphene Fermi energy, the exceptional point can be conveniently located, leading to enhanced spectral sensitivity with small changes in molecular film thickness.