MAGNETIC, SUPERCONDUCTING AND TOPOLOGICAL ORDERS IN IRON-BASED t2g SYSTEM

Iron-based superconductors (FeSCs) are a class set of high-temperature supercon- ductor (HTS) based on different crystal structure and pairing symmetry from the Cu- based HTS. The world’s physicists, chemists and scientists initiated a substantial re- search in studying the mechanisms and details of this new class of HTS. The first goal of studying the FeSCs was to hope that more experimental and theoretical explanation to the origin of superconductivity of similar scenario as in Cu-based HTS. Up to recent years, the underlying mechanism for both the magnetism and superconductivity came to reliable models. However, through out my literature studies, there are still debates in several aspects. I constructed phenomenological model with tight-binding approach for the itinerant picture of electrons, and mean-field self-consistent calculation to study the interacting picture of this model. Point-group-symmetries analysis was also applied to investigate the structure of the model. A proper set of model parameters with correct minimal symmetry analysis well describes the Fermi surface evolution, phase diagram and local density of state (LDOS). To conclude, from chapter 2. to chapter 5., all of my calculated results were nicely compared to experiments and DFT calculations and give deeper understanding to this field. I gave predictions in chapter 6. that new topological phases could exist in the tetragonal crystal structure.