Composite spin-triplet superconductivity in an SU(2) ⊗ SU(2) symmetric lattice model

The two-channel Anderson lattice model which has SU(2) 0 SU(2) symmetry is of relevance to understanding of the magnetic, quadrupolar and superconducting phases in U1-xThxBe13 or Pr based skutterudite compounds such as PrFe4P12 or PrOS4Sb12. Possible unconventional superconducting phases of the model are explored. They are characterized by a composite order parameter comprising of a local magnetic or quadrupolar moment and a triplet conduction electron Cooper-pair. This binding of local degrees of freedom removes the entropy of the non Fermi-liquid normal state. We find superconducting transitions in the intermediate valence regime which are suppressed in the stable moment regime. The gap function is non analytic and odd in frequency: a pseudo-gap develops in the conduction electron density of states which vanishes as \w\ close to w = 0. In the strong intermediate valent regime, the gap function acquires an additional k-dependence.