Coexistence and competition of spin-density-wave and superconducting order parameters in iron-based superconductors

We theoretically study the coexistence of spin density wave (SDW) and superconductivity (SC) in ironpnictide superconductors based on a three-orbital model, focusing on the momentum-space and real-space distributions of SDW and SC order parameters in the coexistence region. We show that a SDW–SC coexisting state lies in the T–n phase diagram, in qualitative agreement with those of NaFe1 − xCoxAs and Ba(Fe1 − xCox)2As2. In the SC state the pairing wavefunction has s ± symmetry with s x 2 y 2 and s x 2 + y 2 components. In the coexisting state, the SDW and SC order parameters display strong orbital-selective competitions in momentum space, which also result in real-space modulation and spin singlet–triplet mixing in the Cooper pairing amplitude. We expect that the obtained features may be observed in future experiments.