Friction of the surface plasmon by high-energy particle-hole pairs: Are memory effects important?

We show that the dynamics of the surface plasmon in metallic nanoparticles damped by its interaction with particle-hole excitations can be modelled by a single degree of freedom coupled to an environment. In this approach, the fast decrease of the dipole matrix elements that couple the plasmon to particle-hole pairs with the energy of the excitation allows a separation of the Hilbert space into low- and high-energy subspaces at a characteristic energy that we estimate. A picture of the spectrum consisting of a collective excitation built from low-energy excitations which interacts with high-energy particle-hole states can be formalised. The high-energy excitations yield an approximate description of a dissipative environment (or "bath") within a finite confined system. Estimates for the relevant timescales establish the Markovian character of the bath dynamics with respect to the surface plasmon evolution for nanoparticles with a radius larger than about 1 nm.Comment: 8 pages, 1 figure; see also cond-mat/070372

Dissipation due to two-level systems in nano-mechanical devices

We analyze the dissipation of the vibrations of nano-mechanical devices. We show that the coupling between flexural modes and two-level systems leads to sub-ohmic dissipation. The inverse quality factor of the flexural modes of low frequencies depends on temperature as $Q^{-1} ( T) \approx Q_{0}+CT^{1/3}$, providing a quantitative description of the experimental data