Untersuchungen zum spinabhängigen ballistischen Transport

Abstract

In this thesis two phenomena of the spin-dependent ballistic transport are investigated theoretically by means of ab initio Korringa-Kohn-Rostocker calculations and an analytical model. The ballistic conductance is evaluated in linear response theory (Landauer formula) by a Green-function formalism. In the first part the hot spots found in ab initio calculations of the kll resolved conductance of tunneling magneto resistance junctions are investigated. Based on an analytical model the full transmission of the electrons in the hot spots is attributed to a resonance effect of interface states on both sides of the barrier. Detailed ab initio studies show that the total conductance can be dominated by the hot spots up to a critical barrier thickness. In the second part one of the fundamental needs for spinelectronics is investigated: the injection of a spin-polarized current into a non-magnetic semiconductor. Here the ballistic spin injection from the ferromagnet Fe into the semiconductors ZnSe and GaAs is calculated for different growth orientations and injection processes. It will be shown that for (001) oriented ideal heterojunctions a nearly 100% spin polarized current is injected into the semiconductor. This can be explained by the symmetry mismatch of the Fe majority and minority states at the Fermi energy