Enhanced Spin Susceptibility toward the Charge-Ordering Transition in a Two-Dimensional Extended Hubbard Model

Abstract

We investigate the charge and spin susceptibilities in the vicinity of a charge-ordering transition point on the basis of a two-dimensional extended Hubbard model with nearest-neighbor Coulomb interaction on a square lattice. In order to evaluate the leading contribution of vertex corrections, we construct a new iterative method generating a series of non-skeleton diagrammatic conserving approximations, and utilize the first approximation for the calculation of response functions. This approximation can determine a charge-ordering transition point and static susceptibilities on an equal footing in a sense that the compressibility and spin-susceptibility sum rules are satisfied. As a prominent effect of vertex corrections, we find that the uniform spin susceptibility is enhanced owing to charge fluctuations that develop toward the charge-ordering transition. We also discuss the experimental relevance of our theory for organic conductors, together with its connection to Landau's Fermi-liquid theory.