UNRESTRICTED SLAVE-BOSON MEAN-FIELD APPROXIMATION FOR THE 2-DIMENSIONAL HUBBARD-MODEL

The Kotliar-Ruckenstein slave-boson scheme is used to allow for an unr estricted variation of the bosonic and fermionic fields on the saddle- point level. Various inhomogeneous solutions, such as spin polarons an d domain walls, are discussed within the two-dimensional Hubbard model and compared with results of unrestricted Hartree-Fock (HF) calculati ons. We find that the present approach drastically reduces the polariz ation of these states and leads to increased delocalized wave function s as compared to the KF model. The interaction between two spin polaro ns turns out to be attractive over a wide range of the on-site repulsi on U. In addition we obtain the crossover from vertical to diagonal do main walls at a higher value of U than predicted by HF.