Size-dependent Correlation Effects in Ultrafast Optical Dynamics of Metal Nanoparticles

TL;DR

This paper investigates how size-dependent surface excitations influence electron relaxation and optical dynamics in small metal nanoparticles, revealing new scattering channels and size-dependent effects on ultrafast spectroscopy.

Contribution

It introduces a size-dependent correction to electron-electron interactions in nanoparticles, highlighting new surface plasmon-mediated scattering mechanisms and their impact on ultrafast optical responses.

Findings

Surface plasmon-mediated scattering rates increase with electron energy.

Size reduction leads to significant changes in absorption lineshape.

Resonant scattering of d-holes affects ultrafast optical dynamics.

Abstract

We study the role of collective surface excitations in the electron relaxation in small metal particles. We show that the dynamically screened electron-electron interaction in a nanoparticle contains a size-dependent correction induced by the surface. This leads to new channels of quasiparticle scattering accompanied by the emission of surface collective excitations. We calculate the energy and temperature dependence of the corresponding rates, which depend strongly on the nanoparticle size. We show that the surface-plasmon-mediated scattering rate of a conduction electron increases with energy, in contrast to that mediated by a bulk plasmon. In noble-metal particles, we find that the dipole collective excitations (surface plasmons) mediate a resonant scattering of d-holes to the conduction band. We study the role of the latter effect in the ultrafast optical dynamics of small nanoparticles and show that, with decreasing nanoparticle size, it leads to a drastic change in the differential absorption lineshape and a strong frequency dependence of the relaxation near the surface plasmon resonance. The experimental implications of our results in ultrafast pump-probe spectroscopy are also discussed.