Abstract:

The coexistence of the spin-density-wave (SDW) and superconductivity in electron-doped iron-pnictide superconductors such as Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$ is studied using a two orbital model which qualitatively reproduces some of the ARPES experimental measurements. Based on the Bogoliubov-de Gennes equations and mean field theory, the phase diagram is mapped out and the evolution of the Fermi surface as the doping varies will be presented. The local density of states (LDOS) has also been calculated from low to high doping. We show that the strength of the superconducting coherent peak at the positive energy gets enhanced and the one at the negative energy is suppressed by the SDW order in the underdoped region. The obtained results are in good agreement with several ARPES and STM experiments. In addition, the doping dependence of the dynamic spin susceptibility is investigated under RPA approximation. Our results for the spin susceptibility are also in good agreement with several neutron scattering experiments in various doping ranges at temperatures above and below the superconducting transition temperature. For the overdoped sample where one of the two hole pockets around $\Gamma$ point disappears according to ARPES, we show that the imaginary part of the spin susceptibility in both SC and normal phases exhibits a gap-like behavior.
 
 
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