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 $(\ensuremath{\sim}1.5\text{ }\text{eV})$ 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.