Transformation optics description of touching metal nanospheres

We present an insightful theoretical description of the optical properties of touching metal nanospheres. Our approach, which exploits transformation optics ideas within the quasistatic approximation, yields simple expressions for all the relevant electromagnetic magnitudes in these singular nanoparticle geometries. We demonstrate the highly efficient collection and concentration of light featured by nanosphere dimers, and show the prominent field enhancement that takes place at the point of contact between a single nanoparticle and a flat metal surface. Our method evidences that surface plasmon modes play a key role in the broadband light harvesting capabilities of these nanostructures. The range of validity of our analytical results are explored through the comparison with numerical full electrodynamic simulations.