Crossover from weakly to strongly correlated regions in the two-dimensional Hubbard model -- Off-diagonal wave function Monte Carlo studies of Hubbard model II --

TL;DR

This study uses improved wave functions in Monte Carlo simulations to explore the 2D Hubbard model, revealing a crossover from weak to strong correlations and potential mechanisms for high-temperature superconductivity.

Contribution

It introduces enhanced wave functions accounting for intersite correlations, providing more accurate ground-state energies and insights into correlation crossover and pairing mechanisms.

Findings

Identifies a crossover from weak to strong correlation regimes as U increases.

Shows reduction of antiferromagnetic correlation with hole doping at large U.

Suggests electron pairing mechanisms related to spin and charge fluctuations.

Abstract

The ground state of the two-dimensional (2D) Hubbard model is investigated by adopting improved wave functions that take into account intersite electron correlation beyond the Gutzwiller ansatz. The ground-state energy is lowered considerably, giving the best estimate of the ground-state energy for the 2D Hubbard model. There is a crossover from weakly to strongly correlated regions as the on-site Coulomb interaction $U$ increases. The antiferromagnetic correlation induced by $U$ is reduced for hole doping when $U$ is large, being greater than the bandwidth, thus increasing the kinetic energy gain. The spin and charge fluctuations are induced in the strongly correlated region. These antiferromagnetic and kinetic charge fluctuations induce electron pairings, which would result in high-temperature superconductivity.