Are the high-Tc superconductors strongly correlated electron systems?
  In this paper, we argue that the high-temperature superconductors do not belong to strong correlated electron systems. It is shown that both the two-dimensional Hubbard and t-J models are inadequate for describing high temperature superconductivity. In our opinion, a superconducting phase should be an energy minimum electronic state which can be described in a new framework where the electron-electron interactions (both on-site Hubbard term and off-site term) and the electron-phonon interaction can be completely suppressed. 
X. Q. Huang
cond-mat.supr-con