VARIATIONAL MONTE-CARLO STUDY OF THE SPIRAL STATE IN THE HUBBARD-MODEL

Choosing the Gutzwiller-type variational wave function and using the variational Monte Carlo (VMC) method, we have calculated the ground-state energies of two-dimensional (2D) Hubbard squares at temperature T = 0 and have obtained the phase diagram in the small doping region (delta = 0-0.15). We do not find the spiral phase until at least U almost-equal-to 20 in the half-filled and dilute-doping cases. This is different from the results obtained by C. Jayaprakash et al., who calculated the phase diagram of the 2D t-J model at temperature T = 0 with the slave-fermion mean-field theory and found the spiral phase at much lower values of U/t.