d-Wave pairing in an ensemble of spin polaron quasiparticles in the spin-fermion model of the electronic structure of the CuO2 plane

• It is demonstrated that d-wave superconducting state could be realized in the ensemble of spin polarons on CuO2-plane.
• The spin polarons Cooper pairing is due to exchange interaction between localized spins on copper ions.
• Simple analytical expressions obtained for spin polaron spectrum both in the normal and superconducting phases.
• The T–x diagram obtained using the spin polaron concept is in good agreement with the experimental data for copper oxides.

It is demonstrated for the first time that the strong coupling between spin moments of copper ions and oxygen holes, which arises upon hybridization mixing of two hole subsystems in the Emery model, not only affects the formation of spin polaron quasiparticles but also ensures effective attraction between them via the exchange interaction. This results in the Cooper instability with d-wave pairing in a 2D ensemble of spin polaron quasiparticles. The T–xT–x phase diagram obtained using this approach agrees well with the available experimental data.