STRONG-COUPLING EXPANSION FOR THE HUBBARD-MODEL

A strong-coupling expansion for models of correlated electrons in any dimension is presented. The method is applied to the Hubbard model in d dimensions and compared with numerical results in d = 1. Third order expansion of the Green's function suffices to exhibit both the Mott m etal-insulator transition and a low-temperature regime where antiferro magnetic correlations are strong. It is predicted that some of the wea k photoemission signals observed in one-dimensional systems such as Sr CuO2 should become stronger as temperature increases away from the spi n-charge separated state.