Phonon absorption of far-infrared radiation in small-metal-particle systems

Abstract

The phonon absorption of small Al spheres is calculated within the jellium model. By taking into account the effect of local jellium-density modulation due to normal modes of elastic oscillations, it is shown that the excitation of a phonon by far-infrared radiation is associated with a transition dipole moment on the order of ${10}^{\mathrm{-}3}$ a.u./sphere. The origin of the dipole, whose magnitude is relatively insensitive to sphere size, can be traced to the incomplete screening of jellium-density modulation near the particle surface. The resulting phonon absorption for a system of 10-Å Al particles is calculated to be comparable in magnitude to Drude absorption at similar frequencies. Conditions for the experimental observation of the effect are discussed.