NMR Study of Highly Correlated Superconductivity
Nuclear magnetic resonance studies on the highly correlated systems such as heavy fermion and high-TC 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-TC 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-TC materials. We will discuss the difference between the heavy fermion and high-TC superconductors.