Double Correlations in HTSC
  The Nambu-Gorkov generalized Hartree-Fock theory of superconductivity is further generalized to treat simultaneously two kinds of correlations: the correlations that lead to superconductivity, as well as the correlations that produce the pseudogap in the normal state. The treatment of these simultaneous double correlations is done by enlarging the dimension of the propagator and self-energy matrices, from two to four. The off-diagonal self-energies and the DOS are calculated. The results are compatible with tunneling and PES experiments. 
Moshe Dayan