Magnetic orders in pnictide superconductors: the effect of biquadratic interaction

The undoped three-orbital spin-fermion model with the additional biquadratic interaction which arises from various factors, such as quantum or thermal fluctuation, is studied using the Monte Carlo method in order to investigate the spin orders in pnictide superconductors. The simulations show that the experimentally observed nematic state can be stabilized by the positive biquadratic interaction, suggesting that such interaction may be another origin for nematicity in pnictides in addition to the couplings to the lattice degrees of freedom. Furthermore, the so-called flux state at low temperatures is identified when a rather weak negative biquadratic interaction is introduced, which is the same as the phase predicted in earlier theoretical work.