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 lambda-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 lambda-zone capacitor allows a blockwise treatment of nano-optical devices and constitutes a basic element of optical nanocircuits.