SEMICLASSICAL THEORY FOR ABSORPTION OF RADIATION IN PARTICLES WITH DIFFUSIVE ELECTRON MOTION

We present a semiclassical analysis for the electric dipole absorption of electromagnetic radiation by small metallic particles, in the case where the electron motion is diffusive. We find that there are two co ntributions to the one-body effective potential: the 'static' potentia l makes a dominant contribution to the absorption coefficient below th e frequency omega(c), = D/a(2), and the 'dynamic' potential is dominan t for frequencies omega much greater than omega(c) (here D is the diff usion constant, and a the size of the particle). Remarkably, these two contributions sum to give exactly the classical absorption coefficien t for all frequencies.