Phase Diagram and Mechanism of Superconductivity in Strongly Correlated Electrons

We investigate the phase diagram of two-dimensional (2D) Hubbard model by employing the optimization variational Monte Carlo method. The 2D Hubbard model is the most simple electronic model for cuprate high-temperature superconductors. The phase diagram consists of three regions; they are antiferromagnetic insulator region, superconducting region, and the coexistent region of superconductivity and antiferromagnetism. The phase diagram obtained by numerical calculations well agrees with the experimental phase diagram for high-temperature cuprates.