INVESTIGATION ON THE GROUND-STATE OF THE HUBBARD-MODEL

The absolute ground states of the Hubbard model are explicitly presented within the framework of pseudospin when U > 2-mu and U < 2-mu. It is shown that the states do not possess true off-diagonal long-range order in the two cases. It is also discovered that in the ground states the U(1) phase symmetry of the Hubbard model is spontaneously broken away from the half-filling, and the total spin is zero, which is independent of the sign of U and the electron filling in the considered periodic lattice.