Magnetic correlations and pairing in the 1/5-depleted square lattice   Hubbard model
  We study the single-orbital Hubbard model on the 1/5-depleted square lattice geometry, which arises in such diverse systems as the spin-gap magnetic insulator CaV4O9 and ordered-vacancy iron selenides, presenting new issues regarding the origin of both magnetic ordering and superconductivity in these materials. We find a rich phase diagram that includes a plaquette singlet phase, a dimer singlet phase, a Neel and a block-spin antiferromagnetic phase, and stripe phases. Quantum Monte Carlo simulations show that the dominant pairing correlations at half filling change character from d-wave in the plaquette phase to extended s-wave upon transition to the Neel phase. These findings have intriguing connections to iron-based superconductors, and suggest that some physics of multiorbital systems can be captured by a single-orbital model at different dopings. 
Ehsan Khatami, Rajiv R. P. Singh, Warren E. Pickett, and Richard T.   Scalettar
cond-mat.str-el