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Abstract:
Plasmonic materials have great potential to enable practical applications in the mid-infrared range and would gain in controllability if they were anisotropic. Here, we report an anisotropic mid-infrared plasmonic metamaterial made of less lossy ZnO:Al (AZO) layers embedded in a dielectric ZnWO4 matrix. The described material exhibits a resonance at the 3-4 μm region, which can be switched on/off by changing light polarisation. Polarisation-dependent reflectance spectroscopy, effective medium and finite-difference time-domain modelling demonstrate that the metamaterial exhibits an epsilon-near-zero (ENZ) hybrid photonic-plasmonic resonance, resembling radiative Berreman modes supported by bulk plasmon polaritons in metal thin films. Remarkably, electric field injection into such layers is realised in a simple far-field experiment without prism or focused beams. Importantly, the material is made with the eutectic solidification, which enables achieving AZO layers through self-organisation process. Additionally, the widely used crystal growth techniques could enable manufacturing metamaterials on a large scale using the eutectic solidification both in the bulk and thin film form. The methodology can be extended to multiple material combination and it opens the way to tuneable infrared metamaterials operating at different wavelengths that can find application such as resonant dichroic filters, reflectors, light-trapping structures, and sensors.