Effects of long-range correlations on nonmagnetic mott transitions in hubbard model on square lattice

The mechanism of Mott transition in the Hubbard model on a square lattice is studied without the explicit introduction of magnetic and superconducting correlations, using a variational Monte Carlo method. In trial wave functions, we consider various types of binding factors between a doubly occupied site (doublon, D) and an empty site (holon, H), like a long-range type as well as a conventional nearest-neighbor type, and add independent long-range D-D (H-H) factors. It is found that a wide choice of D-H binding factors leads to Mott transitions near the bandwidth. We modify the previous the D-H binding picture of Mott transitions by introducing two characteristic length scales, the D-H binding length ℓ_DH and the minimum D-D distance ℓ_DD, which we appropriately estimate. A Mott transition takes place at ℓ_DH = ℓ_DD. In the metallic regime (ℓ_DH > ℓ_DD), the domains of D-H pairs overlap with one another, thereby doublons and holons can move independently by changing their partners one after another. In contrast, the D-D factors give only a minor contribution to a Mott transition.