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

Abstract

It is demonstrated for the first time that the strong coupling between spin moments of copper ions and oxygen holes, which arises upon hybridazation 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 − x-phase diagram obtained using this approach agrees well with the available experimental data.

Coulomb repulsion of holes and competition between $${d_{{x^2} - {y^2}}}$$ d x 2 − y 2 -wave and s-wave parings in cuprate superconductors

“…Solid curve 1 shows the dependence of the critical temperature of superconducting d x 2 −y 2 -wave pairing on the doping level for U p = 0 and V 1 = 0. This curve was obtained earlier in [47] and is in good agreement with experimental data on the absolute value of T c and on the doping region in which the Cooper instability evolves.…”

“…For this purpose, it is convenient to use the Zwanzig-Mori projection method [41][42][43]. The method for calculating the dispersion curves for spin-polaron excitations in the SFM, which is based on this approach, was described in detail in [44] and was actively used in subsequent studies [45][46][47].…”

“…For analyzing the conditions for Cooper instability, we must supplement the above set of three operators with three extra operators [30,47] …”

“…Analysis of system of equations (22) in the normal phase leads to the conclusion that the Fermi excitation spectrum in the SFM is determined by the solutions to the dispersion equation (31) and contains three branches: ǫ 1k , ǫ 2k and ǫ 3k [47]. Lower branch ǫ 1k is characterized by a minimum near point (π/2, π/2) of the Brillouin zone and is separated considerably from the two upper branches ǫ 2k and ǫ 3k .…”

“…This means that in the case of the d-wave pairing and U p = 0, we can obtain instead of system (37) a simpler equation for the superconducting transition temperature T c [47,49,50]. This equation follows from the fifth equation of system (33) and has the form…”