Mixed State in t-U-J-V Model

Abstract

The mean-field approximation (MFA) is one of the most widespread methods in the theory of the condensed matter. It is relatively simple but quite crude, so the need for more refined treatments emerges. One of them is renormalized mean-field approximation (RMFA) [1, 2], similar in use to MFA but in spirit reminding the Gutzwiller method or its slave-boson variations [3]. Applied to Hubbardor t−J-like models amounts to adding a doping-dependent weighting factors both to the hopping and to the interaction parts of the Hamiltonian, followed by the MFA scheme. The hopping-term weighting factor is precisely the band-narrowing factor of the slaveboson theory [4]. In the present paper the RMFA method is applied to the t−U−J−V model in the U → ∞ limit. The results are applicable also to t−J-like models in general. Keeping finite on-site repulsion U during intermediate stages of calculations, to take U → ∞ limit in the end enables us to obtain proper low density limit (i.e., two-electron bound state with finite critical value), incorrectly given in standard t−J model treatment [5]. Considering the V-term is equivalent to using anisotropic t−J model.