NMR study of weak magnetism and superconductivity in heavy-fermion systems

Abstract

Using NMR techniques, we have investigated the superconducting and magnetic properties of the heavy-fermion superconductors (HFS), CeCu 2Si 2, and the recently discovered UM 2AL 3 (M = Ni and Pd). The NMR studies have deduced that the nature of the magnetism in HFS is varied, whereas the superconducting property possesses a rather common feature. Namely, the nuclear spin-lattice relaxation rate 1/ T 1 is well described in terms of an anisotropic energy gap model in which the gap vanishes on lines at the Fermi surface with values of 2 Δ/ k B T c = 5.0 and 5.5 for CeCu 2Si 2 and UPd 2Al 3, respectively. The unusual superconductivity coexists with the magnetism, regardless of whether it is in a static or a dynamical regime. In contrast, the NMR experiment detected no signature of an anomaly at the superconducting transition temperature in UNi 2Al 3. The interplay between magnetism and superconductivity is discussed from a comparison with other heavy-fermion superconductors.