SIZE-DEPENDENT SURFACE-PLASMON DYNAMICS IN METAL NANOPARTICLES

We study the effect of Coulomb correlations on the ultrafast optical d ynamics of small metal particles. We demonstrate that a surface-induce d dynamical screening of the electron-electron interactions leads to q uasiparticle scattering with collective surface excitations. In noble- metal nanoparticles, it results in an interband resonant scattering of d holes with surface plasmons. We show that this size-dependent many- body effect manifests itself in the differential absorption dynamics f or frequencies close to the surface plasmon resonance. In particular, our self-consistent calculations reveal a strong frequency dependence of the relaxation, in agreement with recent femtosecond pump-probe exp eriments. [S0031-9007(98)07279-2].