Excitações coletivas em sistemas eletrônicos quasi-2d via espalhamento inelástico de luz

Abstract

We present a theory for obtaining the inelastic light scattering cross section, Raman scattering, at T = OK temperature in a quasi-bidimensional electron gas formed by the GaAs-A1GaAs semiconductor heterostructure doped selectively. The electronic structure calculations were based on Density Functional Theory within the local density approximation. The calculations for the cross section were performed in backscattering geometry and resonant regime of the incident laser with the spin-orbit optical gap of GaAs . We study charge density excitations mechanism and spin density excitations mechanism. Our results were as follows [1] 1) the observation of the collapse of the Hartree term in the charge density excitation for low densities, observed experimentally by Ernst et al. [2], 2) the observation of an anomalous cross between charge density and spin density excitations, due to the exchange-correlation functional. This effect is a validity test for the adopted parameterizations; 3) the prediction of the existence of excitations of higher energy, not yet observed experimentally. Finally, we demonstrate that the formalism developed enables mapping the electronic excitations in the BCS theory, which describes the normal superconducting state.