Collective versus single-particle effects in the optical spectra of finiteelectronic quantum systems - art. no. 241403

We study optical spectra of finite electronic quantum systems at frequencie s smaller than the plasma frequency using a quasiclassical approach. This a pproach includes collective effects and enables us to analyze how the natur e of the (single-particle) electron dynamics influences the optical spectra in finite electronic quantum systems. We present an analytical expression for the low-frequency absorption coefficient of electromagnetic radiation i n a finite quantum system with regular ballistic electron dynamics; a two-d imensional electron gas confined to a strip of width a with specular reflec tion at the boundaries (our approach is not restricted to systems with regu lar electron dynamics; it applies equally in the case of diffusive or class ically chaotic electron motion). By comparing with results of numerical com putations using the random-phase approximation we show that our analytical approach provides a qualitative and quantitative understanding of the optic al spectrum.