Superconductivity with and without glue and the role of the double-occupancy forbidding constraint in the t-J-V model

Abstract

The occurrence of retarded (with glue) and unretarded (without glue) pairing is thoroughly discussed in cuprates. We analyze some aspects of this problem in the context of the t − J − V model in a large- N approximation. When 1 / N renormalizations are neglected the mean-field result is recovered, where the unretarded d -wave superconducting pairing triggered by the spin-exchange interaction J is obtained. However, the presence of a nonnegligible nearest-neighbors Coulomb interaction V ( q ) kills superconductivity. If the non-double-occupancy constraint and its fluctuations are considered, the situation changes drastically. In this case, V ( q ) is screened making d -wave superconductivity very robust. In addition, we show that the early proposal for the presence of an unretarded pairing contribution triggered by the spin-exchange interaction J can be discussed in this context.