Anisotropy in μ for superconducting aluminum

Using two models for an anisotropic Coulomb pseudopotential parameter mu *(k), approximate upper and lower limits for the anisotropic gap edge of superconducting Al were calculated as a function of wavevector direction over the Fermi surface. All sources of anisotropy, i.e. anisotropic phonon dispersion curves and anisotropic Fermi surface, were considered to determine the electron--phonon spectral functions alpha exp 2 sub k ( omega )F sub k ( omega ) and the matrix elements of the screened Coulomb repulsion. Values of the gap anisotropy parameter < a exp 2 > and of the ratio between the pure single-crystal and isotropic dirty limit critical temperatures were found that agree better with experimental results than the values found using a constant mu *. Disagreement between theory and experiment remains for the variation of Delta sub 0 (k) itself over the Fermi surface. 12 ref.--AA