Localization and screening anomalies in two-dimensional systems

Transport and optical conductivity in dilute magnetic semiconductors

A theory of transport in spin and charge disordered media is developed, with a particular emphasis on dilute magnetic semiconductors. The approach is based on the equation of motion for the current-current response function and considers both spin and charge disorder and electron-electron interaction on an equal footing. The formalism is applied to the specific case of Ga(1-x)Mn(x)As. Within the single parabolic band approximation it is shown that both spin (p-d exchange) and charge (Coulomb) scattering contributions to the resistivity are of the same order of magnitude and should be treated simultaneously. Positional correlations of charged impurities are shown to significantly increase the Coulomb scattering. In the magnetically ordered phase, the suppression of localized spin fluctuations leads to a sizable reduction of spin scattering, which may contribute to the experimentally observed drop in resistivity below the critical temperature. The developed model allows for a comprehensive treatment of electron-electron interaction, screening and correlation effects by means of time-dependent density-functional theory. It is shown that collective modes and a dynamical treatment of electron-electron interaction are essential for an accurate description of the infrared absorption spectrum.

Theory of the linewidth of intersubband plasmons in quantum wells

Intersubband (ISB) plasmons in remotely doped wide quantum wells acquire a linewidth even at zero temperature and in-plane wave vector q(parallel) = 0 by a combination of intrinsic (electron-electron interaction) and extrinsic effects (impurities and interface roughness). We present a quantitatively accurate theory of the linewidth that treats both effects on equal footing and from first principles by a combination of time-dependent density-functional theory with the memory function formalism. Comparison with recent optical absorption experiments shows that the ISB plasmon linewidth has a significant contribution from electron-electron interaction, and is only weakly related to the mobility.