Surface Plasmon Propagation in Thin Metal Films with Epsilon-Near-Zero Transition Layers

The propagation of surface plasmons along metal-dielectric interfaces is studied taking into account the naturally emerging angstrom-sized epsilon-near-zero transition layers at the metal surfaces. Inside the transition layer, a critical point where the dielectric function passes through zero leads to formal divergence of the electric component in a propagating wave, which results in various predicted and observed enhancements in many plasmonic effects and also gives rise to additional collisionless damping of surface plasmon even in an ideal metal.
Here we introduce a novel integral approach to the surface plasmon eigenvalue problem, and we consider cases of both metallic semispace and thin film with finite-width transition layers of arbitrary shape. We show that the problem is not Hermitian and theoretically calculate the damping of the surface plasmon, as well as the correction to its spectrum. We also propose a possible experimental verification of the effects of shifting the position of the singularity point by the applied DC electric field. Based on the numerical simulations, the applied field allows to manipulate the propagation length of the surface plasmon, either decreasing or increasing it, and alter the resonant excitation condition for the plasmon.