Ting, Chin-Sen2016-09-062016-09-06May 20142014-05Portions of this document appear in: Chen, Hua, Yuan-Yen Tai, C. S. Ting, Matthias J. Graf, Jianhui Dai, and Jian-Xin Zhu. "Disorder effects in multiorbital s±-wave superconductors: implications for Zn-doped BaFe 2 As 2 compounds." Physical Review B 88, no. 18 (2013): 184509.Portions of this document appear in: Tai, Yuan-Yen, Jian-Xin Zhu, Matthias J. Graf, and C. S. Ting. "Calculated phase diagram of doped BaFe2As2 superconductor in a C4-symmetry breaking model." EPL (Europhysics Letters) 103, no. 6 (2013): 67001.http://hdl.handle.net/10657/1562Iron-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.application/pdfengThe author of this work is the copyright owner. UH Libraries and the Texas Digital Library have their permission to store and provide access to this work. UH Libraries has secured permission to reproduce any and all previously published materials contained in the work. Further transmission, reproduction, or presentation of this work is prohibited except with permission of the author(s).Iron-basedMagneticsSuperconductorsTopological2016-09-06Thesisborn digital