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Video abstract for the article 'Ultrafast nonlinear dynamics of surface plasmon polaritons in gold nanowires due to the intrinsic nonlinearity of metals ' by A Marini, M Conforti, G Della Valle, H W Lee, Tr X Tran, W Chang, M A Schmidt, S Longhi, P St J Russell and F Biancalana (A Marini et al 2013 New J. Phys. 15 013033). Read the full article in New Journal of Physics at http://iopscience.iop.org/1367-2630/15/1/013033/article. GENERAL SCIENTIFIC SUMMARY Introduction and background. The study of the nonlinear applications of surface plasmon polaritons (SPPs) is a rapidly developing area of research in nanophotonics. Indeed, the subwavelength confinement of SPPs enhances all the nonlinear processes enormously. While the thermo-modulational interband nonlinearity of thin metal films is well-known in the scientific community, its effect on the propagation of SPPs is yet to be described. Main results. We develop analytical and numerical techniques to calculate the thermo-modulational interband nonlinearity of gold and model its effect on the propagation of SPPs on a gold nanowire. Despite the high losses of the fundamental mode, we find a significant red-shift caused by the delayed nonlinearity. Significant red-shift is found also in the propagation of long-range SPPs, where losses are strongly reduced. Wider implications. Our analytical and numerical results demonstrate that, despite the strong metal losses, it is possible to achieve frequency conversion with SPPs propagating in gold nanowires, opening novel possibilities for miniaturized nonlinear devices.