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

Abstract

Motivated by recent experiments in Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ {[}A. E. Böhmer \textit{et al}, to be published{]}, 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. By tracking the magnetic transition line $T_N(x)$ towards optimal doping within an itinerant fermionic model, we find a sequence of transitions 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 the superconducting $T_c$ 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. The full agreement with the experimental phase diagram provides a strong indication that the itinerant approach is adequate to describe the physics of weakly/moderately doped iron-pnictides.

5pp, 2 figures + supplementary material, reference updated