Supersymmetric Mean-field Theory of the t-J Model

[[abstract]]The supersymmetric formulation of the t-J model is studied in this paper at the mean-field level where the δ-T phase diagram is determined. We found that the slave-fermion–like spiral phase is stable at low dopingconcen tration, and the slave-boson–like d-wave fermionic spin pairingstate becomes energetically favourable when δ ≥ 0.23. An improvement in free energy usingGutzwiller’s method lowers the transition dopingconcen tration to δ 0.06. We also point out the existence of new branches of excitations in the supersymmetric theory