On the role of kinematic and exchange interactions in superconducting pairing of electrons in the Hubbard model

Abstract

A system of electrons with strong intra-atomic repulsion U ≫ t in the lower Hubbard subband is considered on the basis of the effective exchange Hamiltonian. An excitation spectrum allowing for the superconducting pairing is obtained by employing the projection technique for the Green function in terms of Hubbard operators. An equation for the gap includes both the kinematic (≈ t) and exchange ( J ≈ t 2/ U) interactions, but only the latter contributes to the d-wave pairing allowed in the strong correlation limit.