NMR Study of Highly Correlated Superconductivity

Abstract

Nuclear magnetic resonance studies on the highly correlated systems such as heavy fermion and high-T_C superconductors are extensively reviewed and both results are compared focusing on the Knight shift and the nuclear spin lattice relaxation time T₁. As for the heavy fermion system, it is presented that the superconductivity coexists with the static magnetic order which has been found for the first time by NMR for CeCu₂Si₂. There are increasing evidences that the superconducting order parameter are uncoventional pointing to the d-wave nature.

As for the high temperature superconductivity, it is pointed out that the superconductivity competes with the static magnetic order and the normal state property is dominated by the antiferromagnetic (A.F.) spin fluctuation possessing two dimensional character. From the NMR investigation, it is shown that the Fermi liquid description is possible for the high-T_C materials as well as in heavy fermion case. Concerning the superconducting property, the identification of the symmetry of the order parameter is still controversial for the high-T_C materials. We will discuss the difference between the heavy fermion and high-T_C superconductors.