On the Dependence of the Superconducting Gap on the Wave Vector in Pr0.89LaCe0.11CuO4

Abstract

The solutions of the Bardeen–Cooper–Schrieffer equation are found within the model of the lower Hubbard subband taking into account three-site correlations and the superexchange, Coulomb, phonon, and spinfluctuation mechanisms of quasiparticle pairing. The Pr_0.89LaCe_0.11CuO₄ compound is considered as an example. The dependence of the superconducting gap on the wave vector along the Fermi contour is approximated by the expression Δ_φ = Δ₀ (B cos(2φ) + (1 − B) cos(6φ)) where the angle φ is measured from the edge of the Brillouin zone. The calculated parameters Δ₀ and B correspond to the experimental data. The role of the phonon mechanism is relatively small. The competition of other specified mechanisms in the formation of Δ₀ is quite strong. The effect of their interference is important and is different in different parts of the Fermi surface. The main contribution to the formation of the component proportional to cos(6φ) (the highest harmonic of the gap) is due to the spin-fluctuation and Coulomb interactions. It is numerically and analytically proved that the role of three-site correlations is reduced to weakening the superexchange mechanism.