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})=Δ₀+Δ₁ cos(4{φ}), where tan({φ})=kₓ/ky. This kind of gap anisotropy predicts a characteristic conductance in electron tunneling, which fits some of the reported experiments.