Observation of propagation of surface plasmon polaritons along line defects in a periodically corrugated metal surface

Propagation of surface plasmon polaritons (SPPs) excited in the wavelength range 720–830 nm at a corrugated gold-film surface with areas of 150-nm-wide and 45-nm-high scatterers arranged in a 380-nm-period triangular lattice containing line defects is investigated by use of near-field optical microscopy. We demonstrate that the SPP at 740–750 nm propagates along $2.2‐\mu \mathrm{m}$-wide and $16‐\mu \mathrm{m}$-long line defects with $\sim 50\%$ loss, whereas its propagation along narrower line defects is strongly damped and in periodically corrugated areas is inhibited. We observe significant deterioration of these effects for both longer and shorter wavelengths and conclude that the SPP guiding occurs as a result of the SPP bandgap effect in the structures.