Properties of a diagonal two-orbital ladder model of the iron pnictide superconductors

We study a diagonal two-orbital ladder model of the Fe-based superconductors using the density-matrix renormalization-group method. At half filling, we find a close competition between a spin-striped state and a noncollinear spin-checkerboard state, as well as significant nematic correlations. Upon finite hole or electron doping, the dominant pairing correlations are found to have A(1g) (S-wave) symmetry.