Spin susceptibility of one-dimensional extended Hubbard model at quarter filling

The ground-state property of one-dimensional extended Hubbard model is investigated at quarter filling. By using spin-charge factorized wave function in the U->∼ limit, the effective exchange coupling Jeff and spin susceptibility χ are calculated as a function of nearest-neighbor Coulomb interaction V. It is found that Jeff is suppressed by the effect of V through charge fluctuation. The results indicate these quantities have no singularities at the transition point because of the Berezinskii-Kosterlitz-Thouless-type transition of charge ordering. We also confirm the results by exact diagonalization method in the realistic parameter range. The relevance to the experiments on quasi one-dimensional organic conductor (DI-DCNQI)2Ag is discussed