Modal Analysis of Deep Nanoscale Plasmonic Structures: Nonlocal Hydrodynamic Approach

Since plasmonic structures at deep-nanometer scale cannot be fully handled by classical electromagnetics, a semiclassical hydrodynamic model has been introduced. The hydrodynamic model essentially describes the motion of the free electron gas in nonlocal metals by imposing additional boundary conditions (ABC). In this work, the hard wall hydrodynamic model with the Sauter ABC is employed, to characterize the optical features of a spherical nanoparticle. The analysis is performed for the natural (quasi-normal) modes of the nanoparticle, supported by the plane wave response of the structure. It is shown that the studied hydrodynamic model provides multiple natural frequencies and natural modes. The natural frequencies are in excellent agreement with extinction resonances.