Generalized cavity model and nonlocal effects in nanoslit arrays

Gap-plasmon resonators are a class of nanogap-based plasmonic structures presenting unprecedented optical properties despite a size that can be smaller than the skin depth of metals. In the case of extremely narrow slit arrays, these ultra-small resonators are better described by a generalized cavity model. Moreover, such structures are sensitive to the nonlocal response of the metals arising from interactions between free electrons inside the jellium. This phenomenon actually influences the necessarily intense plasmonic slowdown (very low phase and group velocities) experienced by the gap-plasmon in such tiny cavities. Accurately describing the optical response of this class of structures requires to take all of these effects into account, and will undoubtedly be necessary to design or characterize future gap-plasmon resonators.