Is the gap anisotropy in high-Tc superconductors really as high as it is commonly believed?

• Published in: Physica. C, Superconductivity Superconductivity, 1996-01, Vol.257 (1-2), p.53-60
• Main Authors: Openov, Leonid A., Elesin, Vladimir F., Krasheninnikov, Arkadiy V.
• Format: Article
• Language: English
• ISSN: 0921-4534; 1873-2143
• DOI: 10.1016/0921-4534(95)00658-3

Making use of the photoemission data on the dependence of the order parameter Δ on the in-plane momentum k and of the tight-binding fit to the Fermi surfaces in hole-doped high-Tc superconductors, we have calculated the anisotropy parameter χ which enters into the formula for Tc versus impurity concentration in an anisotropic s wave superconductor. We have found that χ is as low as ∼ 0.1 in a wide range of hole doping and for different sets of model parameters adjusted to describe the experimental observations of Δ(k) and Fermi surface in Bi2Sr2CaCu2O8+δ. Our results reconcile the large anisotropy of Δ in k space (i.e. not a simple s wave) with the weak sensitivity of Tc to defects and structural inhomogeneities (i.e. probably not a dx2 − y2 wave) and are compatible with the anisotropic s wave symmetry of Δ(k) in hole-doped high-Tc superconductors. Experiments [H. Ding et al., Phys. Rev. B 50 (1994) 1333] on electron irradiation of the twin-free single crystal of YBa2Cu3O7−δ are consistent with a value of χ ≈ 0.3.