ORBITALLY DEGENERATE SPIN-FLUCTUATION MODEL FOR HEAVY-FERMION SUPERCONDUCTIVITY

In this paper, a generalization of standard spin-fluctuation theory is considered by replacing the simple Hubbard interaction by the screened Hartree-Fock interaction for f electrons. This model is then used in both an LS and a JJ coupling scheme to construct the particle-particle scattering vertex. In an on-site approximation, this vertex is shown to lead to an instability for a superconducting pair state which obeys Hunds rules, with L = 5, S = 1, and J = 4, whereas for near-neighbor pairing, the most attractive instability is for J = 0. The degeneracy of these multiplets is broken by anisotropy of the quasi-particle wave functions. Detailed calculations are presented for the case of UPt3.