Doublon–holon-binding mechanism of Mott transition in 2D Hubbard model

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.

► Mechanism of nonmagnetic Mott transitions is studied for Hubbard model by variational Monte Carlo method.
► Previous mechanism by binding between doublon and holon is improved by introducing two characteristic length scales.
► Transition point is detemined by equivalence of these two length scales.