Metal-insulator transition is one of hot issues in condensed-matter physics. The transition between the doped metal and the Mott insulator can be realized in the Hubbard model theoretically. It was recently found that the ground state of the one-dimensional Hubbard model with next-nearest-neighbor hopping clearly shows partial ferromagnetism in the metallic phase near the half-filled Mott insulator. We study the hole density (δ) dependence of the charge susceptibility (χc) of this model by means of exact diagonalization of finite-size clusters. The behavior of the charge susceptibility characterizes the nature of the metal-insulator transition. We find that a region where the critical exponent α defined by χc∝δ-α is α=3 in sharp contrast with the known exponent α=1 in the ordinary one-dimensional Hubbard model.
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