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Magnetic and pairing properties of a two-orbital model for the pnictide superconductors: A quantum Monte Carlo study

Using the constrained-path Monte Carlo method, a two-orbital model for the pnictide superconductors is studied at half filling and in both the electron- and hole-doped cases. At half filling, a stable $(π,0)$/$(0,π)$ magnetic order is explicitly observed, and the system tends to be in an orthomagnetic order rather than the striped antiferromagnetic order when increasing the Coulomb repulsion $U$. In the electron-doped case, the $(π,0)$/$(0,π)$ magnetic order is enhanced upon doping and suppressed eventually, and a $s_{\pm}$ pairing state dominates all the possible nearest-neighbor-bond pairings. Whereas in the hole-doped case, the magnetic order is straightforwardly suppressed and two nearly degenerate $A_{1g}$ and $B_{1g}$ intraband pairings become the dominant ones.