Electromagnetic theory of double Fano resonances in plasmonic nanostructures and metamaterials

The ab initio electromagnetic theory of Fano resonances in resonant plasmonic nanostructures and metamaterials, developed by Gallinet and Martin [Phys. Rev. B 83, 235427 (2011)], is generalized to the case of double Fano resonances. A system is considered in which two uncoupled nonradiative modes interfere with a broad radiative mode driven by incident electromagnetic radiation. Feshbach-Fano partitioning formalism is employed to recover the formula for the double Fano resonance spectral line shape suggested by Fano phenomenologically in his original work, and derive the exact microscopic expressions for the parameters governing the optical response of the system.