SPIN-GAP BEHAVIOR IN HIGH-T(C) OXIDES OBSERVED BY NUCLEAR-SPIN-LATTICE RELAXATION

From the temperature dependence of the nuclear spin-lattice relaxation rate, 1/T1T, in the planar Cu(2) sites, it is found that a highly enh anced and strongly temperature-dependent relaxation process due to-ant iferromagnetic Cu spin fluctuations exists in all high-T(c) supercondu cting oxides. The data also exhibit the opening of a gap in the low-ly ing magnetic excitations with an energy comparable to the superconduct ing gap. In contrast to this T1 behavior, the temperature variations o f the indirectly coupled nuclear spin-spin relaxation rate, 1/T2g, and the anisotropic Knight shifts K(alpha) have quite an independent sign ature; the former shows continuous increase toward T(c) and the latter in the low low-doping regime decreases from a much higher temperature than that at which the spin-gap is seen in 1/T1T. These features indi cate that the generalized spin susceptibility, chi(q, omega), has very characteristic temperature variations for different q and omega regio ns.