Theoretical study of disorder and proximity effects in three-dimensional models of topological insulators

Resumen

This PhD manuscript mainly covers the theoretical study of the electronic properties of Bi2Se3 family topological insulators, in presence of different defects and proximity effects with a graphene layer. All calculations are based on density functional theory (DFT) method, tight binding (TB) and effective continuum models which allow to obtain simultaneously a realistic description of electronic properties of clean materials, but also to explore the impact of defects and disorder on such properties. Regarding the study of disorder, we have particu-larly scrutinized the impact of rotation mismatches inside the quintuple structure and the ef-fect of surface hydrogenation on the properties of ultrathin TI structures. Besides that, the effect of both non-magnetic and magnetic chemical impurities have been investigated using the generic TB Fu-Kane-Mele (FKM) model of three-dimensional TI in the context of gap opening and changes of the spin textures of the surface states. By varying the density of impurities and their magnetic orientation, a series of conclusions could be made on gap features and evolving spin textures of surface states. Finally, the properties of graphene/TI heterostructures have been studied using DFT and a TB model, fitted to the first-principles calculations. The presence of a spin transport anisotropy was found to be a smoking gun of the proximity effect of the TI on the graphene states, a result which has been also discussed in the context of experimental measurements.