Lattice Zenneck Modes on Subwavelength Antennas

Optical resonances in isolated nanoparticles made out of commonly occurring materials with high optical losses, such as transition metal dichalcogenides, germanium, carbide, and others, are weak and not sufficient for field enhancement and competing with plasmonic resonances in noble metal nanoparticles. This work presents a novel approach to achieve strong resonances in the arrays of such nanoparticles with large optical losses and points to their potential for efficient light control in ultra-thin optical elements, sensing, and photovoltaic applications. Materials with large imaginary part of permittivity (LIPP) are studied and nanostructures of these materials are shown to support not only surfaces modes, known as Zenneck waves, but also modes localized on the subwavelength particle. This approach opens up the possibility of exciting strong localized nanoparticle resonances without involving plasmonic or high-refractive-index materials. Arranging LIPP particles in a periodic array plays a crucial role allowing for collective array resonances, which are shown to be much stronger in particle array than in single particle. The collective lattice resonances can be excited at the wavelength defined mainly by the array period and thus easily tuned in a broad spectral range not being limited by particle permittivity, size, or shape.