Surface-plasmon polaritons in a lattice of metal cylinders

Plasmon modes of a two-dimensional lattice of long conducting circular wires are investigated by using an embedding technique to solve Maxwell’s equations rigorously. The frequency-dependent density of states is calculated for various values of the wave vector and the filling fraction. At low filling fractions, collective modes are all found to accumulate at the surface-plasmon frequency ω_p∕√2, ω_p being the bulk plasmon frequency. As the filling fraction increases, the interference between the electromagnetic fields generated by localized surface-plasmon polaritons leads to the presence of new resonances, whose frequency strongly depends on the interparticle separation. For touching wires, a number of multipole resonances fill the spectral range between dipole resonances, as occurs in the case of a three-dimensional packing of metal spheres.