NaV_2O_5 as an Anisotropic t-J Ladder at Quarter Filling

TL;DR

This paper models NaV_2O_5 as an anisotropic quarter-filled t-J ladder, revealing its Mott insulating state and charge instability due to inter-ladder Coulomb interactions, aligning with experimental findings.

Contribution

It maps the electronic states of NaV_2O_5 to an anisotropic t-J ladder and analyzes charge and spin properties, providing a theoretical framework consistent with experiments.

Findings

NaV_2O_5 modeled as an anisotropic t-J ladder in Mott insulating state

Effective exchange interaction J_eff matches experimental estimates

Inter-ladder Coulomb repulsion causes charge instability

Abstract

Based on recent experimental evidences that the electronic charge degrees of freedom plays an essential role in the spin-Peierls--like phase transition of NaV$_2$O$_5$, we first make the mapping of low-energy electronic states of the $d$$-$$p$ model for NaV$_2$O$_5$ 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, of which lowest-energy states can be modeled by the one-dimensional Heisenberg antiferromagnet 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.