Anomalous resonances in properly shaped plasmonic nanostructures can in principle lead to infinite absorption/gain efficiencies over broad bandwidths of operation. By developing a closed-form analytical solution for the fields scattered by conjoined hemicylinders, we outline the fundamental physics behind these phenomena, associated with broadband adiabatic focusing of surface plasmons at the nanoscale. Over a continuous frequency range, our proposed composite nanostructure shows finite amount of absorption/amplification even in the limit of infinitesimally small intrinsic material loss/gain. Detailed physical insights are provided to justify the nature of this apparent paradox, and its counterintuitive behavior is discussed for potential applications in nonlinear optics, spasing, sensing, and energy-harvesting devices.
N. Mohammadi Estakhri and A. Alù, “Physics of Unbounded, Broadband Absorption/Gain Efficiency in Plasmonic Nanoparticles,” Physical Review B, Vol. 87, No. 20, 205418 (9 pages), May 10, 2013. https://doi.org/10.1103/PhysRevB.87.205418.
American Physical Society