Problems of RVB theory of high-Tc superconductivity

For understanding the mechanism of the high-Tc superconductivity it was very important to observe that in the Hubbard model the strong correlation of electrons due to their on-site Coulomb repulsion is the origin of an attractive effective pairing interaction of some quasi-fermions. Subsequently it was shown that this pairing interaction gives rise to the appearance of a superconducting gap in the electron energy spectrum. On the basis of this physical phenomenon the RVB theory of high-Tc superconductivity generated by the strong correlation of electrons has been proposed and widely discussed. Although the real mechanism might be rather complicated and would contain the pairing interactions of different origins, the strong correlation of electrons always plays a crucial role in the theory of ceramic high-Tc superconductors