An Orbitally Degenerate Spin Fluctuation Model for Heavy Fermion Superconductivity

TL;DR

This paper develops a generalized spin fluctuation model incorporating screened interactions for f electrons, predicting a Hund's rule obeying superconducting state with specific angular momentum properties, applied to UPt3.

Contribution

It introduces a generalized spin fluctuation framework using screened Hartree-Fock interactions and applies it to heavy fermion superconductors like UPt3.

Findings

Predicts a superconducting instability obeying Hund's rules

Shows degeneracy breaking due to anisotropy in quasiparticle wavefunctions

Provides detailed calculations for UPt3

Abstract

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. The degeneracy of this state is broken by anisotropy of the quasiparticle wavefunctions. Detailed calculations are presented for the case of $UPt_3$.