Crossover-Induced Spin Fluctuation and Electron Pairing in Strongly Correlated Electrons

Abstract

We investigate the two-dimensional (2D) Hubbard model and d-p model as a model for cuprate high-temperature superconductors, by employing an optimized variational Monte Carlo method. We improved the many-body wave function starting from the simple Gutzwiller function. On the basis of optimized variational wave functions, we show that there is a superconducting phase in the ground state of the 2D Hubbard model. The on-site repulsive Coulomb interaction U can bring about high-temperature superconductivity because its characteristic energy is of the order of eV. The attractive interaction between electrons is induced by the crossover from weakly to strongly correlated regions. High-temperature superconductivity is possible in the strongly correlated region, where U is greater than the bandwidth.