Superconductivity of Heavy Fermions in Valence Fluctuating Systems

Abstract

On the basis of the Fermi liquid description of the normal state, singlet (s-symmetry) superconductivity in the Kondo lattice is examined near its transition temperature. For the criterion of superconductivity, a focus is given on the competition between the pair weakening force due to the spin fluctuation and the attractive interaction between neighboring f electrons. This competition explains that α-Ce is a normal Fermi liquid under ambient pressures, while it becomes superconducting under high pressures. It is also argued that singlet superconductivity is likely to be realized in CeCu₂Si₂ from the pressure dependence of the transition temperature, or the dependence of the transition temperature on the Kondo temperature.