Optical nonlocalities and additional waves in epsilon-near-zero metamaterials.

We analyze the optical properties of plasmonic nanorod metamaterials in the epsilon-near-zero regime and show, both theoretically and experimentally, that the performance of these composites is strongly affected by nonlocal response of the effective permittivity tensor. We provide the evidence of interference between main and additional waves propagating in the room-temperature nanorod metamaterials and develop an analytical description of this phenomenon. Additional waves are present in the majority of low-loss epsilon-near-zero structures and should be explicitly considered when designing applications of epsilon-near-zero composites, as they represent a separate communication channel.

Optical transmission measurements of silver, silver-gold alloy and silver-gold segmented nanorods in thin film alumina.

Silver nanorods have been grown by electrodeposition into thin film porous alumina. Transmission measurements show two peaks related to the transverse and longitudinal resonance of the nanorods. The behaviour of the longitudinal resonance peak is found to vary with nanorod length and the spectral position to depend on nanorod diameter. As the distance between the nanorods is decreased a small blue-shift of the longitudinal peak is observed. Depositing a small gold cap on top of the silver nanorods causes a red-shift of the longitudinal peak whilst, conversely, the longitudinal peak of gold nanorod arrays is comparatively insensitive to the deposition of a silver cap. Gold-silver alloy nanorods were also deposited from a mixed salt bath and a linear dependence of the transverse peak position on alloy composition was observed.