Broadband metacoaxial nanoantenna for metasurface and sensing applications.

We introduce a metacoaxial nanoantenna (MN) that super-localizes the incident electromagnetic field to "hotspots" with a top-down area of 2 nm(2), a local field enhancement of ~200-400, and a field localization with a very large spectral range from the visible to the infrared range that has a spectral bandwidth ≥ 900 nm. Not only is this nanoantenna extremely broadband with ultra-high localization, it also shows significant improvements over traditional nanoantenna designs, as the hotspots are re-configurable by breaking the circular symmetry which enables the ability to tailor the polarization response. These attributes offer significant improvements over traditional nanoantennas as building blocks for metasurfaces and enhanced biodetection that we demonstrate in this work.