Epsilon-near-zero media coupled with localized surface plasmon modes

Epsilon-near-zero (ENZ) media are an emerging platform, embracing the great potential for novel nanophotonic phenomena. One method to obtain an ENZ medium is to operate at the cutoff wavelength of the fundamental mode of a plasmonic waveguide. Control over this mode is limited to the waveguide's material and size properties. Here, we demonstrate that a plasmonic nanostructure (nanorod) can be strongly coupled to the plasmonic waveguide, providing two new hybrid resonance modes exhibiting characteristics of both guided ENZ modes and localized surface plasmon modes. Strong coupling gives rise to a Rabi splitting of 300 meV, which is demonstrated by finite-difference time domain simulations where we calculate the decay rate enhancement of a dipole emitter located in the coupled system. The hybrid modes are retrieved using the analytic coupled harmonic oscillator model. This suggested method via hybridization of modes can be used to generate and manipulate ENZ media where the unique ENZ property of wavelength extension enables effectively shrinking spatially long distances down to optically short distances.