Undamped plasmon-polariton propagation along metallic nano-chain including nonlinear effects
The nonlinear theory of collective plasmon-polariton propagation along the infinite chain of metallic nanoparticles is developed within RPA quasiclassical approach to surface plasmons in large nano-spheres (10-50 nm for radius) of Au or Ag. The wave type self-modes in the chain are determined and analyzed with respect to nano-sphere size and chain-separation parameters. At some regions for parameters the undamped modes occur. They were found on the rim of stability within the linear theory. The nonlinear corrections stabilize, however, diverging modes of the linear approach and considerably enlarge the region of undamped propagation. Nonlinearity is associated with relativistic corrections to the Lorentz friction. According to the nonlinear behavior, the region of parameters when undamped stable modes occur, covers the instability region of the linear theory. The remarkable property of fixed amplitude of the undamped collective propagating wave independently of initial conditions (even if they are extremely small) has been identified and described. The group velocity of this wave propagation is calculated.