Ultimate limit of field confinement by surface plasmon polaritons

We show that electric field confinement in surface plasmon polaritons propagating at metal/dielectric interfaces enhances the loss due to Landau damping, which effectively limits the degree of confinement itself. We prove that Landau damping, and associated with it surface collision damping, follow directly from the Lindhard formula for the dielectric constant of a free electron gas. Furthermore, we demonstrate that even if all of the conventional loss mechanisms, caused by phonons, electron-electron interactions, and interface roughness scattering, were eliminated, the maximum attainable degree of confinement and the loss accompanying it would not change significantly compared to the best existing plasmonic materials, such as silver.