The mechanism of nonmagnetic Mott transitions in the Hubbard model on the square lattice is studied, using a variational Monte Carlo method. A simple doublon (D)-holon (H) binding mechanism a previous study proposed [J. Phys. Soc. Jpn. 75 (2006) 114706] has to be modified, because even a wave function with completely bound D-H pairs brings about a Mott transition at a finite correlation strength. By introducing two characteristic lengths, D-H pair binding length, ξDH, and minimum inter-doublon distance, ξDD, we can properly describe the physics of Mott transitions, and determine the critical point by ξDD ∼ ξDH. This concept seems universal, because it is valid not only for newly introduced wave functions with long-range D-H and D-D (H-H) correlation factors discussed here, but for a wide range of wave functions with D-H binding factors.
- Hubbard model
- Mott transition
- Variational Monte Carlo method