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Supplementary Effects of Fluorine Doping and Pressure on Electronic Structure of LaO1-xFxFeAs Superconductor

Ebrahimi, Mohammad Reza | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 46320 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Khosroabadi, Hossein; Akhavan Farshchi, Mohammad
  7. Abstract:
  8. Iron based superconductors that are studied more in recent years, have the same and different features with copper oxide high temperature superconductors which they can help in solving problems related to high temperature superconductors. In addition, these compounds have attractive physical characteristics such as superconductivity despite of presence of magnetic Iron element or other magnetic elements like nickel and cobalt (In other superconductivity groups, low doping of magnetic elements destroys superconductivity) and also concurrent presence of magnetic and superconductivity phases. The most reported transition temperature in these compounds is 56.3K in Gd0.8Th 0.2FeAsO compound. Calculating of band structure and momentum resolved spectral function analysis of LaOFeAs compound by density functional theory and dynamical mean filed theory shows that this compound is a bad metal in normal situation. By doping Fluorine Ions in place of oxygen Ions, we can increase the conductivity of this material, Meanwhile we can increase the superconductivity transition temperature to 26 k. Therefore, we can expect that this material's transition temperature increases using mechanical pressure. It has been shown theoretically that pressure equal to 4Gpa on LaO1-xFxFeAs ,which x=0.11 (optimal doping) we can increase transition temperature of this material to 43K that it has high importance. Despite high endeavors for offering a complete theory for vindicating superconductivity in these materials, but like copper oxide superconductors, they have faced challenges.
    In regard to this fact that pressure effect and Fluorine doping in LaoFeAs compound and its effect on creating superconductivity and optimizing superconductivity of transition temperature, for understanding each of them, we can study the correlation between these two parameters based on structural and electron specifications of this compound. The goal of this thesis is theoretical study of supplementary effects of fluorine doping and pressure based on density functional theory by quantum espresso software.first, we calculate band structure,density of states and Fermi surface of this compound for doping levels x=0,x=0.25 and x=0.5 .then in order to study supplementary effects we apply pressure on compounds with doping levels x=0.25 and x=0.5 , we see there is a optimum pressure in which density of states is maximum and then with further increasing pressure density of states decrease.The results of this calculations are used to explain experimental data related to this compound
  9. Keywords:
  10. Density Functional Theory (DFT) ; Pressure ; Iron Based Superconductor ; Electron Structure ; Fluorine Doping

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