Figure 1
Comparison of confinement and loss properties of surface plasmon polaritons propagating on niobium (a, blue diagram), gold (b, green diagram) and silver (b, purple diagram), assuming that the metal films are sandwiched between two semi-infinite silica layers.
In the three left-handed performances maps (a–c), the hatched areas refer the regions of subwavelength confinement (δ < λ0/2) of the SR-SPP mode. The filled colored regions indicate the domain of long-range propagation (Labs > 1000 λ0, long-range regime) of the LR-plasmon. The vertical dotted blue line in Fig. 1a indicates the thickness of the niobium film used in the experiments. The properties of the complex dielectric functions of the three discussed materials (Nb: blue, Au: green, Ag: purple) are shown in the two right-handed diagrams ((d): real parts of dielectric function (solid lines), (e) corresponding imaginary parts (dashed curves)).
