Polarization-Controlled Nanogap Cavity with Dual-Band and Spatially Overlapped Resonances

Metasurfaces are ultrathin, two-dimensional arrays of subwavelength resonators, which can possess optical properties unobtainable naturally. One such desirable property is dual-band absorption occurring at the same spatial location, which could enable the enhancement of multiple processes simultaneously. However, demonstrations of multiband absorption to date have been limited to the mid-infrared and microwave regimes. Here, metasurfaces are demonstrated to have spatially overlapped, dual-band absorption in the visible to near-infrared using arrays of plasmonic nanogap cavities that consist of a sub-10 nm dielectric layer sandwiched between gold rectangles and a gold film. The relative strength of the two modes is tuned dynamically by varying the incident polarization, and the period between elements is used to tune the spectral bandwidth. Additionally, these near-perfect absorber structures fabricated by electron beam lithography (EBL) are compared to similar nanogap geometries fabricated using colloidal...