FERMION MEAN-FIELD SOLUTIONS FOR THE HEISENBERG AND THE T-J MODELS

Fermion mean-field solutions for the Heisenberg and the t-J models have been obtained by considering particle-hole correlations and carrying out the mean-field-theory calculations in momentum space. At half-filling the solutions have mixed (s+/-d)-wave-like symmetry and have a lower ground-state energy than the s (uniform phase) and the d phases. On doping, the solutions with mixed s and d symmetry still have lower ground-state energy than the uniform phase. In the presence of doping, the density of states at the Fermi level in the mixed phases is depressed from its value in the uniform phase and is in good agreement with the experimental data.