Estudo dos efeitos de confinamento quântico em semicondutores magnéticos e isolantes topológicos

Abstract

In this thesis, we use first-principles calculations based on density functional theory to study quantum confinement effects on magnetic semiconductors and topological insulators. Because there are variety of systems with These classifications, we have selected InAs quantum dots embedded in InP nanowires and Bi(111) ultrathin films. For InAs quantum dots, we show that ferromagnetic coupling Mn-Mn is stronger than nanowires and InAs bulk, and this is still higher than in GaMnAs bulk. The stabilization of the ferromagnetic phase is a consequence of the strong p-d exchange between the Mn 3d5 states and the hole bound to the magnetic impurity. This magnetic active system is governed mostly by short-range interactions in such a way that the coupling between Mn ions at the same quantum dot is quite robust while Mn ions at neighboring dots is weaker. For Bi(111) ultrathin films we showed that, while a single Bi bilayer is a 2D TI with 1D topological conduction, few bilayers of Bi is a 3D TI, presenting massless Dirac cone on the surface, with 2D topological conduction