NaV_2O_5 as an Anisotropic t-J Ladder at Quarter Filling

Abstract

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 be 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.