THE COMPETITION BETWEEN SUPERCONDUCTIVITY AND SPIN DENSITY WAVE IN Ba1-xKxFe2As2 SUPERCONDUCTOR

ABSTRACT This thesis focuses on the study of the competition between superconductivity and spin density wave in Ba1-xKxFe2As2 superconductors using two band model Hamiltonian. The model Hamiltonian for the system develops using the concept of BCS theory through Bogoliubov transformation formalism; we have to obtain the mathematical expressions of superconducting transition temperature, spin density wave transition temperature, spin density wave order parameter and Superconductor order parameter. By employing the theoretical and experimental value of the parameters in the obtained expression we draw graphs to more clarify the final mathematical expressions and show the relationship between the parameters. In detailed we observed that in pure superconductive state the superconducting order parameter suppressed when temperature increases and vanished at a temperature equals to superconductive critical temperature of Ba1-xKxFe2As2. In pure spin density wave state, a spin density wave order parameter also becomes decay exponentially as temperature increases and becomes zero at the temperature equals to superconducting transition temperature. In our compound Ba1-xKxFe2As2 we can also described superconducting transition temperature becomes decrease exponentially as the spin density wave ordered parameter increases but the spin density wave transition temperature increases exponentially when spin density wave order parameter becomes increases. Finally by taking a common axis for spin density waves order horizontally and put the superconducting transition temperature in one side and spin density wave transition temperature on the other side of the vertical axis we can draw the graphs and show the competition between superconductivity and spin Density wave in Ba1-xKxFe2As2.