Gossamer superconductivity and antiferromagnetism in the t-J-U model -: art. no. 104505

The d-wave superconductivity (dSC) and antiferromagnetism are analytically studied in a renormalized mean-field theory for a two-dimensional t-J model plus an on-site repulsive Hubbard interaction U. The purpose of introducing the U term is to partially impose the no-double-occupancy constraint by employing the Gutzwiller approximation. The phase diagrams as functions of doping delta and U are studied. Using the standard value of t/J=3.0 and in the large-U limit, we show that the antiferromagnetic (AF) order emerges and coexists with the dSC in the underdoped region below the doping delta similar to 0.1. The dSC order parameter increases from zero as the doping increases and reaches a maximum near the optimal doping delta similar to 0.15. In the small-U limit, only the dSC order survives while the AF order disappears. As U increases up to a critical value, the AF order shows up and coexists with the dSC in the underdoped regime. At half-filling, the system is in the dSC state for small U and becomes an AF insulator for large U. Within the present mean-field approach, we show that the ground-state energy of the coexistent state is always lower than that of the pure dSC state.