  Using the negative U Hubbard model we analyze normal state properties of a
superconductor. In this model there exists a characteristic pairing temperature
T_P above a superconducting critical temperature. Below T_P electrons start to
form incoherent pairs. The fluctuations in charge and phase are precursors of
charge density wave and superconductivity phases depending on band filling.
They lead naturally to pseudogap opening in the density of states.

Superconductivity;Strongly Correlated Electrons