LOCAL SPIN CLUSTERING AND PHASE-SEPARATION IN THE HUBBARD-MODEL

We use an unrestricted self-consistent mean-field approach to the one-dimensional periodic Hubbard model to study its ground-state phase diagram. Our approach allows one to incorporate spin and electron correlations as well as spin and charge fluctuations. We find that a homogeneous antiferromangetic state exists only at half-filling, where the state is also insulating. Off half-filling, it was found that the ground state of the Hubbard model consists of clusters with different magnetic and charge properties. For certain values of the parameters of the system the cluster formation develops to a full phase separation. The effects of the intersite repulsive or attractive interaction on the ground-state properties were also examined. Implications of our results for the existence of a superconducting ground state as well as comparison with other studies will be briefly discussed.