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Subwavelength localization and toroidal dipole moment of spoof surface plasmon polaritons

2015; American Physical Society; Volume: 91; Issue: 3 Linguagem: Inglês

10.1103/physrevb.91.035116

1550-235X

Seong‐Han Kim, Sang Soon Oh, Kap‐Joong Kim, Jae‐Eun Kim, Hae Yong Park, Ortwin Hess, Chul‐Sik Kee,

Photonic Crystals and Applications

We experimentally and theoretically demonstrate subwavelength scale localization of spoof surface plasmon polaritons at a point defect in a two-dimensional groove metal array. An analytical expression for dispersion relation of spoof surface plasmon polaritons substantiates the existence of a band gap where a defect mode can be introduced. A waveguide coupling method allows us to excite localized spoof surface plasmon polariton modes and measure their resonance frequencies. Numerical calculations 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, we find that 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. In addition, the dispersion properties of spoof surface plasmon polaritons are analyzed using a modal expansion method and numerical calculations.