  Starting from first principles, we theoretically model the nonlinear temporal
dynamics of gold-based plasmonic devices resulting from the heating of their
metallic components. At optical frequencies, the gold susceptibility is
determined by the interband transitions around the X,L points in the first
Brillouin zone and thermo-modulational effects ensue from Fermi smearing of the
electronic energy distribution in the conduction band. As a consequence of
light-induced heating of the conduction electrons, the optical susceptibility
becomes nonlinear. In this paper we describe, for the first time to our
knowledge, the effects of the thermo-modulational nonlinearity of gold on the
propagation of surface plasmon polaritons guided on gold nanowires. We
introduce a novel nonlinear Schroedinger-like equation to describe pulse
propagation in such nanowires, and we predict the appearance an intense
spectral red-shift caused by the delayed thermal response.
