Quasiparticle interactions and nature of pairing in heavy fermions.

Transport and thermodynamic experiments have verified the suggestion that superconductivity in heavy Fermions is not of the conventional type. A detailed examination of these results reveals an anisotropic superconducting state with line(s) of zeroes of the gap function. A phenomenological theory with pairing due to exchange of antiferromagnetic fluctuations is shown to lead to anisotropic singlet states with such properties. Microscopic examination of the interaction of two Kondo impurities leads to such antiferromagnetic interactions in the asymptotic low temperature Fermi-liquid.