Estudo por primeiros princípios das propriedades estruturais e eletrônicas dos compostos Bi2Te3 e Bi2Se3

Abstract

The understanding of the physical properties of topological insulators has been a very active field in the past few years. These materials are strong candidates for spintronics applications due to their unusual electronic properties. In this text, we present a brief introduction to the theory concerning these materials, and an abinitio study of the electronic and structural properties of the compounds Bi2Te3 and Bi2Se3. First, we discuss the quantum spin-Hall effct and an effective model to describe the 2D and 3D topological insulators. After that, we present the methodology of the density functional theory, which was employed in our calculations, and we discuss two distinct problems. In the first one, we worked with the experimental group of Prof. Rogério Paniago (Physics department, UFMG) in order to investigate the surface termination of the topological insulator Bi2Te3 after cleavage, and after a thermal treatment. Our results suggest that a bismuth bilayer appears on the top of the surface. In the second work, carried out in collaboration with the surface physics group from UFMG, we studied the structural properties of the topological insulator Bi2Se3. We show that there is not a significant structural reconstruction between superficial layers, which interact by van der Waals forces, and, therefore, this fact should not be responsible for the presence of additional electronic states which are observed in these compounds after cleavage.