Unconventional Superconductivity and Magnetism in Lanthanide and Actinide Intermetallic Compounds

In this review article we present a survey of unconventional superconductors and their coexistence behaviour with magnetism. We focus on Ce- and U-based heavy fermion superconductors, in addition we discuss the rare earth borocarbide and skutterudite superconductors. We show that heavy fermion behaviour in Ce- and U- compounds should be described differently. While the Kondo-lattice model with localised 4f-electrons is appropriate for Ce-compounds, dual models including localised and itinerant 5f-electrons are necessary for U-compounds. We demonostrate that this leads to consistent results for Fermi surface topology and mass enhancement in various U-compounds. We also show that virtual exchange of localised 5f-electron excitations provides a new mechanism for unconventional superconductivity in addition to the known itinerant spin-fluctuation exchange mechanism. We discuss symmetry properties and coexistence of unconventional superconducting and density wave (hidden) order parameters and methods for their detection, notably the new angle resolved magntetotransport methods. The latter have been very succesful for the investigtion of gap anisotropies in the nonmagnetic borocarbide superconductors. Recent results on the new multiphase Pr-skutterudite superconductor are also reviewed.