Effects of charge ordering on the spin degrees of freedom in one-dimensional extended Hubbard model

The effects of charge ordering on the spin degrees of freedom is studied by using one-dimensional extended Hubbard model. The ground state property is investigated in the U → ∞ limit using spin-charge factorized wave function. The effective exchange coupling J_eff and spin susceptibility χ are calculated as a function of nearest neighbor Coulomb interaction V for several electron densities. It is found that J_eff is suppressed by the effect of V through charge fluctuation and, as a result, χ increases with increasing V. Furthermore, χ at T = 0 has no detectable anomaly at the transition point where a charge ordering occurs, because of the Berezinskii-Kosterlitz-Thouless (BKT) type transition of charge ordering. We also calculate χ by exact diagonalization on small clusters in realistic parameter range and obtained qualitatively the same results. These results mean that the charge fluctuation play important roles around the transition point and the charge ordering has little effect on the spin degrees of freedom. The relevance to experiments on (DI-DCNQI)₂Ag is briefly discussed.