Tetragonal magnetic order and superconductivity in iron pnictides

Multiband and multiorbital physics is crucial for understanding superconductivity and magnetism in iron pnictides. We employ a realistic multiorbital model to study the newly discovered tetragonal magnetic phase in Ba_x-1Na_xFe₂As₂ and Ba_1-xK_xFe₂As₂.This additional fourfold symmetric phase is observed in Ba_x-1Na_xFe₂As₂ by neutron powder diffraction close to the suppression of the spin-density-wave (SDW) order and is in agreement with the scenario of magnetically driven nematic order. We elucidate the role played by orbital effects and compare them to other multiorbital systems. Furthermore, we study the coexistence and competition of tetragonal magnetic order and superconductivity as well as the possibility of additional phase transitions in this regime.