Local capacitor model for plasmonic electric field enhancement

We present a local capacitor model that enables a simple yet quantitatively accurate description of lightning rod effect in nanoplasmonics. A notion of λ-zone capacitance is proposed and applied to predict the strongly induced electric field by a light source near nanoscale metal edges such as metal tip or metal gap. The enhancement factor, calculated from the local capacitor model, shows excellent agreement with more rigorous results. The λ-zone capacitor allows a blockwise treatment of nano-optical devices and constitutes a basic element of optical nanocircuits.