|
Title
|
|
|
|
First-principles studies of novel two-dimensional dirac materials
| |
|
Author
|
|
|
|
| |
|
Abstract
|
|
|
|
| Graphene is the most famous 2D Dirac materials since 2004. In the past ten years, the study of graphene make large contributions to theory, experiment, and applications. Its influence is not only in physics, but also in many other fields. From the point of view of the Dirac band structure of graphene, this thesis address one main question: Can we find other elements forming a stable 2D lattice with Dirac points? For the question, we proposed three different kinds of 2D Dirac materials. Using first-principles calculations, we predicted a new stable carbon monolayer, H4,4,4-graphyne. Adding the adjacent element of C in the periodic table, i.e. the N element, two kinds of dumbbell C4N structures can be obtained. The three monolayers all can be called C-based materials. They all show Dirac band structures with a linear relationship between E and k and the SOC effect is too weak much that we can neglect it. These C-based monolayers show high Fermi velocities, making them become promising materials for future high-speed electronic devices. Remarkable, the Fermi velocities of H4,4,4-graphyne are slightly higher than that of graphene. To our knowledge, the Fermi velocities of H4,4,4-graphyne are the highest Fermi velocities among all of the 2D carbon structures. On the other hand, we tried to find some materials exhibiting a large SOC effect. Since it is difficult to see the SOC effect in materials containing only light elements, we focused on materials having heavy elements, such as Bi. We proposed several Bi-based 2D topological insulators. The large nontrivial band gaps make it possible to realize the QSH effect at room temperature. Remarkable, we found Dirac points when changing the SOC strength. Although large SOC effect can be found in those Bi-based 2D topological insulators, they do not show any magnetic properties. Considering magnetic proprieties, we tried transition metals and we predict a spinpolarized Dirac point in Y-based materials. Due to the transition metal Y, ferromagnetic properties can be found. The bands of spin-up and spin-down are separated and the Dirac point formed by the spin-down bands is at the Fermi level. Including SOC, a large nontrivial band gap is opened. The proposed Chern insulator 1T-YN2 can be used to realized QAH effect. |
| |
|
Language
|
|
|
|
English
| |
|
Publication
|
|
|
|
Antwerpen
:
Universiteit Antwerpen
,
2019
| |
|
Volume/pages
|
|
|
|
152 p.
| |
|
Note
|
|
|
|
:
Peeters, François M. [Supervisor]
| |
|
Full text (open access)
|
|
|
|
| |
|