On the nature of “multi-petal” structure and anomalous temperature dependence of anisotropic gap in high-temperature superconductors

Abstract

It is shown that the observed in ARPES experiments anisotropic “multi-petal” structure of the superconducting gap Δ in the plane of the CuO2 layers in Bi2Sr2CaCu2O8+x may be a result of strong anisotropy of the electronic spectrum, originated in the hybridization of the broad and narrow 2D bands. Prevailing Coulomb repulsion between electrons from the different portions of the anisotropic Fermi-surface leads to different signs of the superconducting gap in symmetry directions Γ-M and Γ-X(Y) of the Brillouin zone, as well as to zero values of the gap in the intermediate directions. The temperature dependence of the gap in Γ-X(Y) directions, obtained in the framework of the model of superconductor with multi-component order parameter, differs drastically from the standard BCS form of Δ(T), and agrees with the experimental data.