ELECTRIC-DIPOLE ABSORPTION BY BALLISTIC ELECTRONS IN SMALL METAL SPHERES

We describe a semiclassical approach to estimating the absorption of e lectromagnetic radiation by small conducting spheres, in which the mot ion of the charge carriers is ballistic. The results are strikingly di fferent between the cases of rough and smooth walled particles. For a rough walled particle the absorption coefficient is proportional to om ega(2) in the low-frequency limit. For a smooth walled sphere the abso rption coefficient has a low-Frequency cut-off at omega(c), the angula r frequency of a circumferential 'whispering gallery' classical orbit of a carrier at the Fermi surface. At frequencies above omega(c) the s pectrum consists of a sequence of overlapping resonance bands which co mbine to give an absorption coefficient proportional to omega(2) only for omega much greater than omega(c).