Significant advance in the field of nanophotonics has been achieved with the help of metamaterials - artificially created composite structures, whose electromagnetic properties drastically differ from the properties of the natural materials. However, three-dimensional metamaterials are poorly compatible with planar technology, which is a significant obstacle for their applications in the optical range. One of the possible ways to overcome this problem is to use metasurfaces, a two-dimensional analogue of metamaterials. Along with unprecedented control over reflected and transmitted waves and provide precise engineering of phase, amplitude, polarization, propagation direction, and wavefront of electromagnetic field.
In the framework of effective medium approximation, anisotropic metasurface can be described by a two-dimensional conductivity tensor. The dispersion relation can be directly derived from the Maxwell's equations by using effective conductivity tensor. We provide an experimental approach which allows to determine effective conductivity tensor of the particular metasurface, and predicts coexistence of unusual surface waves with TE-, TM- and hybrid polarizations.
In the present work we analyzed spectrum of the surfaces waves propagating along plasmonic metasurfaces consisting of anisotropic gold subwavelength particles placed on a silica substrate. We have shown that the spectrum of plasmonic metasurfaces consists of two hybrid polarized quasi-TE and quasi-TM surface modes which could have very high directivity and demonstrate non-diverging propagation. The strong anisotropy of the gold particles could result in appearance of a hyperbolic regime of the metasurfaces at the frequencies closed to the plasmonic and Mie resonances of the gold particles, respectively.
We provided an experimental study of surface waves localized on plasmonic metasurface and fully confirm our theoretical findings. In addition to the quasi-TE and quasi-TM modes predicted theoretically we observed a near dispersionless surface mode. We have shown that this mode is formed due to the interaction of quadrupole resonances of the gold nanoparticles.
