Propagation of collective surface plasmons in 1D periodic ionic structure
The propagation of the collective surface plasmons, called plasmon-polaritons, in infinite equidistant ionic sphere chain has been analyzed. The ideal cancellation of irradiative losses of these ionic excitations in the chain is demonstrated by inclusion of appropriately retarded near-, medium and far-field components of dipole interaction between spheres in the chain. It is proved that the Lorentz friction losses in each sphere are completely compensated by the energy income from the rest of the chain for a wide sector of the plasmon-polariton wave vector domain. There is shown that the damping of plasmon-polariton is reduced to only residual Ohmic losses much lower than irradiation losses for the separate electrolyte sphere. The self-frequencies and the group velocities of plasmon-polaritons for longitudinal and transversal (with respect to the chain orientation) polarizations are determined and assessed for various ion and electrolyte parameters. It is proved that there exist weakly damped self-modes of plasmon-polaritons in the chain for which the propagation range is limited by relatively small Ohmic losses only. Completely undamped collective waves are also described in the case of the presence of persistent external excitation of some fragment of the chain. The possibility of application of the plasmon-polariton model to describe the so-called saltatory conduction in periodically myelinated nerve axons is preliminarily discussed.