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

•Obtaining a coexistence phase of superconductivity and spin-density-wave in a three-orbital Hamiltonian for iron pnictides.•The two coexisting orders display strong orbital-selective competitions in momentum space.•The competition also result in real-space modulation of the superconducting order parameter and singlet–triplet mixing.

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±s± symmetry with sx2y2sx2y2 and sx2+y2sx2+y2 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.