Anisotropic energy gaps in copper oxide superconductors

Gap anisotropy is discussed for a two-dimensional superconductor on a square lattice. For s-wave pairing the simplest form of anisotropy is Δ(φ)=${\Delta }_0$+${\Delta }_1$ cos(4φ), where tan(φ)=$k_x$/$k_y$. This kind of gap anisotropy predicts a characteristic conductance in electron tunneling, which fits some of the reported experiments.