Boosting the Magnetic Response of a Composite Nanostructure in the Near‐Visible Region with a Fano Resonance

Plasmonic nanostructures can show a magnetic response in addition to an electrical one by guiding the plasmonic displacement current along a circular loop, inducing a magnetic dipole. Achieving a magnetic response at optical frequencies requires composite nanostructures with multiple elements to prevent saturation effects. A composite nanostructure consisting of three nanorods is presented that form a split‐ring resonator with two additional gaps. The optical behavior of this nanostructure is investigated with both numerical simulation and experimental fabrication and measurement. Moreover, it is demonstrated that adding a nanorod below the central element facilitates an additional dark magnetic mode that causes a Fano resonance in the structure, increasing the magnetic near‐field enhancement and the overall magnetic response of the nanostructure.