Static Spin Susceptibility with Anisotropic Superconducting Gap Parameter in High-TcCu Oxides

The wave-number dependent BCS spin susceptibility χ( q ) with various-type anisotropic superconducting gap parameters Δ( q ) is calculated for a two dimensional nearly antiferromagnetic Fermi liquid model with the random-phase-approximation (RPA). The Δ( q ) anisotropic but gapful on the Fermi surface gives rise to a significant reduction of χ( q ) around q = Q [=(π,π)]. The enhanced χ( q ∼ Q ) below T c as large as above T c can be traced to the d ( x 2 - y 2 )-wave gap parameter or the nodeless anisotropic gap parameter with the specific minimum gap, Δ m i n (0.35<2 Δ m i n / k B T c <0.7), on the Fermi surface. From the experimental findings on the enhanced χ( q ∼ Q ) below T c and the anisotropic Δ( q ) on the Fermi surface for the high- T c Cu oxides, we conclude that the d ( x 2 - y 2 )-wave gap parameter is realized but not the other types in the high- T c superconductivity, except the additional change of the order parameter.