Slow-plasmon resonant nanostructures: Scattering and field enhancements

Resonances in metal nanostructures supporting propagation of slow surface plasmon-polariton (SPP) modes are considered. Resonant enhancements in scattering and built-up electric fields of nm thin submicron-wide metal strips are investigated using a surface integral equation method and ascribed to the excitation of strip-cavity modes formed by short-range SPPs. A properly positioned narrow gap (5 nm) in the strip is found to lead, by virtue of boundary conditions, to significant field enhancement (similar to 30, inside the gap), as well as to a noticeable (similar to 10%) blueshift in the resonance wavelength.