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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