  This work investigates the relation between superconductivity and
correlations. A simple calculation shows that the appropriate spin-charge
correlation is the key role to any superconductivity, and this calculation is
consistent with the analyses of unusual properties of superconductors. (Note:
the Tc of this model is not given clearly in this work, but we have advanced
this mechanism to a t-x model which includes various superconductivities and
magnetisms (please see arXiv:0707.3660 and following works).)
