Time-Domain Ab Initio Study of Phonon-Induced Relaxation of Plasmon Excitations in a Silver Quantum Dot

Abstract

Relaxation of plasmon excitations through the phonon channel is investigated in a silver nanocrystal with a surface-hopping Kohn–Sham density functional theory in the time domain. Good agreement with the experimental data is obtained. Plasmons delocalize away from the nanocrystal core and couple to a narrow range of low-frequency acoustic phonons. Higher energy plasmon excitations tend to be more delocalized, exhibit weaker coupling to phonons, and relax more slowly than lower energy plasmons. The phonon-induced plasmon relaxation occurs on a picosecond time scale. This is two orders of magnitude longer than the time scale of elastic plasmon–phonon scattering, which contributes to the line-width of plasmon resonances via the pure-dephasing mechanism. The phonon-induced energy relaxation of plasmons in metallic particles is somewhat slower than that of charge carriers in semiconducting nanoscale materials. The difference can be attributed to the extended nature of plasmon excitations, resulting in a weaker interaction with phonons and coupling only to low-frequency vibrations.