Magnetism and superconductivity in heavy-fermion compounds (abstract)

Abstract

The mean-field theory based on an extended high degeneracy model is derived to describe an interplay between the Kondo effect, magnetism, and superconductivity in heavy-fermion compounds. The competition and coexistence of the Kondo effect and ferro- or antiferromagnetic orders of localized moments are considered depending on the local exchange interaction. It is shown that an antiferromagnetic order arising in the coherent Kondo state can have an anomalously small antiferromagnetic moment per f atom (∼0.01μB) and stimulate superconductivity with an anisotropic superconducting gap that vanishes along lines on the Fermi surface. We apply the theory for studying thermodynamic peculiarities of the antiferromagnetic and superconducting transitions, and the microscopic structure of the antiferromagnetic and superconducting states in URu2Si2 and UPt3. The theoretical estimation (0.035μB) of the antiferromagnetic moments of U atoms in URu2Si2 is in good agreement with the experimental result (0.04μB). We also study the microscopic origin of the double superconducting transition in UPt3. The superconducting gap in the successive superconducting states is strongly anisotropic. In the former state the gap vanishes on part of the Fermi surface, while in the following state the gap vanishes on lines only.