Subwavelength scale localization of spoof surface plasmon polaritons at a point defect in a two-dimensional groove metal array to exhibit a band gap where a defect mode can be introduced is demonstrated in experiments and numerical simulations. To excite localized spoof surface plasmon polariton modes and measure their resonance frequencies, a waveguide coupling method was employed. Experimental and numerical simulation results confirm that localized modes can have a very small modal volume and a high Q factor both of which are essential in enhancing light-matter interactions. Interestingly, the localized spoof surface plasmon polariton has a significant toroidal dipole moment, which is responsible for the high Q factor, as well as an electric quadrupole moment.
cskee@gist.ac.kr