Optical Forces in Plasmonic Nanoparticle Dimers

Abstract

We present calculations of the optical forces between two metal nanospheres forming a hybridized plasmonic dimer. We consider homo- and heterodimers and investigate different plane wave illumination configurations. The forces between the particles are calculated using full Mie theory combined with the Maxwell stress tensor (MST) formalism, as well as by approximate methods, such as the Lorentz force (LF) approach taken in the dipole limit and calculations based on an optical potential. We show that the simplified calculation schemes can lead to serious errors in the case of strongly interacting particles and low damping. In particular, we find that equilibrium configurations, corresponding to vanishing optical forces, only are possible for homodimers illuminated in the end-fire configuration and for heterodimers, although multipolar effects and damping radically reduce the repulsive interactions in the latter case.