We study the localization of plasmonic modes on topological dislocations obtained by an abrupt change in the geometry of unit cells in a plasmonic metasurface comprised of a nanoscale array of rectangular apertures. We experimentally demonstrate mode localization in line defects and point singularities in the topology. These results are confirmed by numerical simulations of the near field distributions along the topology boundaries. We present structures with line dislocations supporting dark and bright modes. Moreover, we show that in structures with point dislocations the localization strength can be further manipulated by modifying the topological order of the structure.

Broken mirror symmetry of chiral structures imposes a lack of mirror symmetry in the scattering profile. When an energy dissipation channel is introduced in the system, an overall optical activity arises. Plasmonic nanostructures, therefore, are an ideal platform to induce optical activity by means of constitutional or configurational chirality. We experimentally investigate the mechanism of plasmonically induced configurational chirality in a periodic monoclinic hole array with a broken mirror symmetry. The resulting optical activity of the structure is studied by using k-space leakage radiation measurements.

We examine the Kramers–Kronig relations between the circular dichroism and the optical rotation dispersion in the k-space obtained from a chiral metasurface with a reduced rotational symmetry. We operate a leakage-radiation microscopy system to probe the near-field plasmonic modes and measure the polarization effects of the grating. By using our system we were able to capture and analyze the plasmonic modes at both air/gold and gold/glass interfaces. The k-space mapping of the chirality parameters allows us to fully analyze the optical activity of the metasurface. We experimentally find that the reduction in rotational symmetry affects the locality condition which unavoidably leads to the deviation from the Kramers–Kronig relation.

The phenomenon of coupling between light and surface plasmon polaritons requires specific momentum matching conditions. In the case of a single scattering object on a metallic surface, such as a nanoparticle or a nanohole, the coupling between a broadband effect, i.e., scattering, and a discrete one, such as surface plasmon excitation, leads to Fano-like resonance lineshapes. The necessary phase matching requirements can be used to engineer the light–plasmon coupling and to achieve a directional plasmonic excitation. Here, we investigate this effect by using a chiral nanotip to excite surface plasmons with a strong spin-dependent azimuthal variation. This effect can be described by a Fano-like interference with a complex coupling factor that can be modified thanks to a symmetry breaking of the nanostructure.

Light–matter interactions in a chiral structure can induce strong polarization selectivity. Specifically, an optical activity in a form of polarization rotation and a circular dichroism may be controlled by the mirror symmetry breaking of the unit-cell geometry. We design and experimentally investigate plasmonic metasurfaces with a spatially varying chiral geometry and demonstrate how this architecture may lead to a geometric Berry phase. Our designed structure produces a polarization-dependent diffraction of nearly linear states. We experimentally examine the diffraction orders and show that they are topological in nature. Moreover, the influence of various geometrical factors is also investigated.