Superconductivity and Phase Separation in Extended Hubbard Model

Having cuprate superconductors in mind, we study the effect of intersite repulsion on antiferromagnetism (AF) and superconductivity (SC) in an extended Hubbard model on a square lattice with a diagonal transfer t′, using a variational Monte Carlo method. In the trial wave function, essential factors for Mott physics and band renormalization are included. It is found by introducing small intersite repulsion that the SC dome shrinks but AF is almost unchanged for U/t=10 (likely for cuprates). Meanwhile, instable range of doping rate (δ) toward phase separation becomes narrower. This instable range of δ almost coincides with the range of a finite AF gap, especially in good coincidence for t′/t=0.