Reduced damping of surface plasmons at low temperatures

We investigated the effectiveness of low temperatures in reducing plasmon damping by measuring the homogeneous linewidth of plasmon resonances (similar to 1.5 eV) in nanoscale gold bipyramids at temperatures from 293 to 6 K. The linewidth drops linearly with temperature and approaches a constant value at approximately 50 K. Measurements were performed on monodisperse ensembles as well as on single particles. The 30% decrease in the homogeneous linewidth with decreasing temperature is well accounted for by the reduced electron-phonon scattering. The other relaxation mechanisms-electron-electron scattering, electron-surface scattering, and radiative relaxation-do not change significantly with temperature.