Tandem Pairing in Heavy Fermion Superconductors

We examine the internal structure of the heavy fermion condensate, showing that it necessarily involves a d-wave pair of quasiparticles on neighboring lattice sites, condensed in tandem with a composite pair of electrons bound to a local moment, within a single unit cell. These two components draw upon the antiferromagnetic and Kondo interactions to cooperatively enhance the superconducting transition temperature. The tandem condensate is electrostatically active, with a small electric quadrupole moment coupling to strain that is predicted to lead to a superconducting shift in the NQR frequency.