PHYSICAL PROPERTIES OF NANOMATERIALS: WITH APPLICATIONS TO PENTAGONAL SYSTEMS

Abstract

In this thesis we theoretically study a set of novel systems, known as pentagonal materials. Physical properties of interest such as electronic structure, optical response, electronic transport properties and the existence of topological phases are analyzed. We have employed well-established techniques as well as innovative approaches in order to get a detailed picture of all the mentioned features. The structure of the work is described next. In Part I we present the theoretical concepts that are used throughout the entire thesis. Such topics are symmetry basics, with group theory generalities, first-principles methods, the tight-binding approximation, optical response in the tight-binding approximation, electronic transport in the ballistic regime and topological properties of materials. The exposition is brief, highlighting only the needed concepts for the subsequent parts. Part II concerns with the electronic, optical and transport properties of penta-graphene (PG) and its nanostructures. We show how penta-graphene responds to an electromagnetic field perturbation analyzed within the tightbinding approach. We also compute features of the electronic structure of penta-graphene and its nanostructures by means of first-principles and tightbinding methods. We obtain good accordance between these two approaches in electronic and optical response. Also, a promising thermoelectric transport performance is found for a particular device configuration. Part III includes the theoretical study and numerical calculation of symmetryenforced and topological properties of pentagonal materials. We use several examples of PG-derived systems by doping or adsorption. This allows us to design different phases such as trivial metallic phases with nodal lines, Dirac nodes in presence of spin-orbit coupling and time-reversal symmetry breaking phases with a non-trivial Chern insulator character. Identification of additional phases like Weyl nodes, weak and crystalline topological phases is also feasible. Topological properties were studied by the calculation of topological invariants with the Wannier charge center evolution method and also by a recent theoretical framework called topological quantum chemistry. Considering all the results obtained in this work, we can assert that pentagonal materials represent a promising family of low dimensional systems with many interesting physical properties that deserve to be studied in more detail in upcoming years.