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

Abstract

Motivated by experiments in ${\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{K}}_{x}{\mathrm{Fe}}_{2}{\mathrm{As}}_{2}$ [A. E. B\ohmer et al., 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 ${T}_{c}$ in the coexistence phase with SDW magnetism. We find a sequence of transitions, upon lowering the temperature, from the stripe-orthorhombic $({C}_{2})$ SDW order to the tetragonal $({C}_{4})$ order and then back to the ${C}_{2}$ order. We argue that ${T}_{c}$ has two discontinuities---it jumps to a smaller value upon entering the coexistence region with the ${C}_{4}$ magnetic phase, and then jumps to a larger value inside the SDW state when it crosses the boundary between the ${C}_{4}$ and ${C}_{2}$ 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.