NaV2O5 as an anisotropic t-J ladder at quarter filling

Based on recent experimental evidences that the electronic charge degrees of freedom play an essential role in the spin-Peierls-like phase transition of NaV2O5; we first make the mapping of low-energy electronic states of the d - p model for NaV2O5 to the quarter-filled t - J ladder with anisotropic parameter values between legs and rungs, and then show that this anisotropic t - J ladder is in the Mott insulating state: the lowest-energy states of which can he modeled by the antiferromagnetic Heisenberg chain with the effective exchange interaction J(eff) whose value is consistent with experimental estimates. We furthermore examine the coupling between the ladders as the trellis lattice model and show that the nearest-neighbor Coulomb repulsion on the zigzag-chain bonds can lead to the instability in the charge degrees of freedom of the ladders.