  The electronic states of the two-dimensional Hubbard model are investigated
by means of a 4-pole approximation within the Composite Operator Method. In
addition to the conventional Hubbard operators, we consider other two
operators, which come from the hierarchy of the equations of motion. These
operators carry information regarding surrounding spin and charge
configurations. By means of this operatorial basis, we can study the physics
related to the energy scale J=4t^2/U. Results present, in addition to the main
two bands, a quasi-particle peak at the Fermi level, shadow bands and band
flatness at (pi, 0) point.

Strongly Correlated Electrons