Interplay between tetragonal magnetic order, stripe magnetism, and superconductivity in iron-based materials

Motivated by experiments in Ba1-xKxFe2As2 [A. E. Böhmer, arXiv:1412.7038], we analyze the type of spin-density wave (SDW) order in doped iron-pnictides and the discontinuities of the superconducting transition temperature Tc in the coexistence phase with SDW magnetism. We find a sequence of transitions, upon lowering the temperature, from the stripe-orthorhombic (C2) SDW order to the tetragonal (C4) order and then back to the C2 order. We argue that Tc has two discontinuities - it jumps to a smaller value upon entering the coexistence region with the C4 magnetic phase, and then jumps to a larger value inside the SDW state when it crosses the boundary between the C4 and C2 SDW orders. We argue that the agreement with the experimental phase diagram provides a strong indication that the itinerant approach is adequate for weakly/moderately doped iron pnictides.