Charge Ordering and Spin Gap in NaV_<b>2</b>O_<b>5</b>

Abstract

A possible ground state of NaV 2 O 5 is proposed based on the Hartree approximation for both on-site and intersite Coulomb interactions. The results indicate that the intersite Coulomb interaction induces a zigzag type of charge disproportionation (i.e., charge ordering) along the ladders of V ions, resulting in localized spins between neighboring ladders to form a spin gap. This new state, which is different from the spin-Peierls state so far believed, seems to be consistent with the existing experimental results.