NMR-STUDY IN NOVEL SUPERCONDUCTORS - HEAVY-FERMION SYSTEM AND HIGH-T-C CUPRATE

From the NMR and NQR studies we show the unconventional superconductin g properties in the antiferromagnetic (AF) heavy-fermion (HF), UPd2Al3 and high-T-c cuprate systems. In UPd2Al3 with T-N=14.5 K and T-c=2 K, the superconductivity is shown to be of d-wave pairing type with line s of vanishing gap on the Fermi surface. The potential scattering asso ciated with some defects at the Al site is the cause for the T-c suppr ession and the appearance of the density of states (DOS) at the Fermi level. This unusual impurity effect is consistent with a d-wave scenar io, because the potential scattering leads to a gap opening for an ani sotropic s-wave scenario. In high-T-c cuprate which are argued to be e ither a d-wave or an anisotropic s-wave, the potential scatterer like Zn in the plane induces the gapless superconductivity as well, which c an not be interpreted in terms of an anisotropic s-wave scenario if th e order parameter does not change sign largely. It is shown from the N MR experiment at the Al site for Al-doped La1.85Sr0.15CuO4 that local moments at near neighbor Cu sites induced around Al impurity do not pl ay a role to suppress the T-c and to induce the DOS at all. The NMR st udies in novel superconductors have provided important clues to identi fy their symmetry of order parameter to be d-wave.