The meaning of strange momentum structures in the gap

The anisotropy of the superconducting gap is usually associated with the an isotropy of the pairing scattering, and in the exception of the gap symmetr y structure, like the nodes, it is expected to be smooth and predictable. T here is, however, the alternative approach of momentum decoupling (dominant ly forward scattering), in which the anisotropy of the gap follows the anis otropy of the electronic density of states in all gap symmetries. In this l ast case, the gap can have strange anisotropies in addition to the symmetry -related nodes. We argue that the hump centered in the Gamma-X direction of the Bi2212 gap seen in ARPES, reflects the corresponding hump in the elect ronic 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 directi on disappears (a situation plausible in the Momentum Decoupling regime). Th is correlation of the gap anisotropy with the DOS anisotropy implies a quas i-Kronecker momentum structure for the scattering amplitude. (C) 1999 Elsev ier Science B.V. All rights reserved.