The meaning of strange momentum structures in the gap

The anisotropy of the superconducting gap is usually associated with the anisotropy of the pairing scattering, and in the exception of the gap symmetry structure, like the nodes, it is expected to be smooth and predictable. There is, however, the alternative approach of momentum decoupling (dominantly forward scattering), in which the anisotropy of the gap follows the anisotropy of the electronic density of states in all gap symmetries. In this last case, the gap can have strange anisotropies in addition to the symmetry-related nodes. We argue that the hump centered in the Γ–X direction of the Bi2212 gap seen in ARPES, reflects the corresponding hump in the electronic density of states when for overdoped and/or contaminated samples the gap symmetry is switched from d-wave to s-wave and the node in this direction disappears (a situation plausible in the Momentum Decoupling regime). This correlation of the gap anisotropy with the DOS anisotropy implies a quasi-Kronecker momentum structure for the scattering amplitude.