Supersymmetric mean-field theory of the t-J model

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 doping concentration, and the slave-boson-like d-wave fermionic spin pairing state becomes energetically favourable when δ ≥ 0.23. An improvement in free energy using Gutzwiller's method lowers the transition doping concentration to δ ≃ 0.06. We also point out the existence of new branches of excitations in the supersymmetric theory.