Abstract
The f electrons of cerium and uranium compounds are localized at the atomic sites and the indirect f-f interaction is mediated by the spin polarization of the conduction electrons and enhances the long-range magnetic order, which is known as the RKKY interaction. On the other hand, the Kondo effect quenches the magnetic moments of the localized f electrons by the spin polarization of the conduction electrons. The competition between the RKKY interaction and the Kondo effect forms the heavy fermions at low temperatures. The localized-f electronic state is thus changed into an f-derived band with a flat dispersion, possessing an extremely large effective mass. These conduction electrons condense into a new superconducting state, which is highly different from the conventional BCS type. It is also noted that in these compounds the electronic states are tuned by magnetic fields and pressures because the characteristic temperatures are low.
