Fig. 4

Wave-vector diagrams and surface-plasmon field distributions. a Phase-matching point (solid, black vertical line) for metamaterial/dielectric interface, and wave-vector diagram displayed in the (k _t , γ _n )-coordinate system. The red curve corresponds to wave-vector components (k _t , γ _n ) in the dielectric side and the blue curve in the metamaterial side. The solid curve denotes evanescent waves and the dashed curve indicates propagating waves. b SP-field profile (H _z , red), and the relative amplitude and orientation of normal and tangential component of E-field (right). Note the loose confinement of SP field and the dominance of normal E-field. c Phase-matching point (black vertical line) at bulk metal/dielectric interface. d SP-field profile (H _z , red) and the relative amplitude and orientation of normal and tangential components of E-field (right). Note the strong confinement of SP field and the dominance of tangential E-field in metal side