Nuclear Magnetic Resonance in Heavy Fermion Systems

Abstract

Heavy-fermion (HF) systems discovered in rare-earth or actinide intermetallic compounds have been the intriguing subject of experimental [1,2,3] and theoretical [4] investigations. At low temperature, these systems having very large specific-heat coefficient and Pauli like susceptibility are characteristic of a strongly interacting electronic fermi liquid with heavy effective mass, which is derived from 4f- or 5f-electrons behaving as localized electrons at high temperature. It has become increasingly evident that the system has a new and unique ground state. The most outstanding and fascinating aspect is the fact that the compounds such as CeCu₂Si₂ [5], UBe₁₃ [6] and UPt₃ [7] exhibit a transition to the superconducting state. The superconducting properties are unusual, indicating that the heavy electrons are responsible for the superconductivity. Considerable amounts of experimental evidences, which conflict with the conventional theory, have suggested that the energy gap in these compounds is anisotropic, vanishing at points or lines on the Fermi surface [8,9,10,11]. First, these compounds have been discussed in analogy to superfluid ³He-A phase where the gap zeros of points are associated with the anisotropic triplet Cooper pairing. Subsequently, there have been many experimental and theoretical investigations to gain an insight into the nature and the mechanism of Cooper pairing of HF superconductor.