On the instability and phase separation of a doped 2D antiferromagnet

Abstract

A mean-field decoupling for the Schwinger bosons and slave fermions in a t-J model shows that at small dopings the thermodynamic potential (with fixed chemical potential) of a doped 2D antiferromagnet is higher than that of an undoped one. At zero temperature the threshold doping beyond which doped states have lower potentials is δ t≅0.3 for t/J=3−4. The violation of the particle number constraint at the mean-field level is further improved via a generalized Gutzwiller approach in which a two-site reduced density matrix is employed. This substantially modifies the energy, the thermodynamic and the chemical potentials, but δ t remains roughly the same. Our result may be related to the instability and phase separation of the system discussed in the literature.