Doped singlet-pair crystal in the Hubbard model on the checkerboard lattice
Résumé
In the limit of large nearest--neighbor and infinite on--site Coulomb repulsion, the Hubbard model on the planar pyrochlore lattice maps, near quarter-filling, onto a doped quantum fully packed loop model. The phase diagram exhibits at quarter filling a novel quantum state of matter, the Resonating Singlet-Pair Crystal, an insulating phase breaking lattice symmetry. Properties of a few doped holes are investigated. In contrast to the doped quantum antiferromagnet, phase separation is restricted to very small hopping leaving an extended''window'' for superconducting pairing. However the later is more fragile for large hopping than in the case of the antiferromagnet.