Long-Range Correlation of Electron Pairs in the Hubbard Model at Finite   Temperatures in Three Dimensions
  We show that in the translation invariant case and in the antiferromagnetic phase, the reduced density matrix $\rho _2$ has no off-diagonal long-range order of on-site electron pairs for the single-band Hubbard model on a cubic lattice away from half filling at finite temperatures both for the positive coupling and for the negative coupling. In these cases the model can not give a mechanism for the superconductivity caused by the condensation of on-site electron pairs and the nearest-neighbor electron pairs. 
Gang Su and Bao-Heng Zhao