Coexistence of dx2-y2 superconductivity and antiferromagnetism in the two-dimensional t-J model and numerical estimation of Gutzwiller factors

The coexisting phase of the d-wave superconducting and the antiferromagnetic order in the two-dimensional t-J model is reexamined using a variational Monte Carlo method in order to estimate the Gutzwiller factors. A trial wave function is used which is consistent with the mean-field solution. The Gutzwiller factors are determined by comparing the numerically obtained expectation values with the mean-field values. We find the z component of the Gutzwiller factor of exchange interaction is enhanced compared with the xy components. This effect does not appear in the conventional Gutzwiller approximation and is essential for the stabilization of the antiferromagnetic order in the presence of d-wave superconductivity. We discuss several applications of the present Gutzwiller factors to the problems with antiferromagnetism and d-wave superconductivity. [S0163-1829(99)51538-5].