Undamped collective surface plasmon oscillations along metallic nanosphere chains

The random-phase-approximation semiclassical scheme for describing plasmon excitations in large metallic nanospheres (with radius ∼ 10 - 60 nm ) is developed for the case when a dynamical electric field is present. The spectrum of plasmons in metallic nanospheres is determined including both surface and volume-type excitations and their mutual connections. It is demonstrated that only dipole-type surface plasmons can be excited by a homogeneous dynamical electric field. The Lorentz friction due to irradiation of electromagnetic energy by plasmon oscillations is analyzed with respect to sphere dimension. The resulting shift in resonance frequency due to plasmon damping is compared with experimental data for various sphere radii. Wave-type collective oscillations of surface plasmons in long chains of metallic nanospheres are described. The undamped region for collective plasmon propagation along the metallic chain is found in agreement with previous numerical simulations.