NMR-STUDY OF HIGH-TC SUPERCONDUCTORS

From systematic measurements of T1, Knight shift, NQR frequency of Cu-63 and O-17 with high-pressure measurement in high-T(c) materials, La2-xSrxCuO4, YBa2Cu3O7 and Tl2Ba2CuO6+y the following results have been obtained. The staggered susceptibility at the zone boundary, chi(Q) which is a measure of the antiferromagnetic spin fluctuation decreases in order of the La, Y and Tl system. Chi(Q) is governed by the number of Cu d-holes, n(Cu) and O p-holes, n(O) in the CuO2 plane. Chi(Q) increases when n(Cu)/n(O) increases. T(c) increases and then decreases with n(Cu)/n(O) having a maximum at an optimum value of n(Cu)/n(O). Correlation between chi(Q) and T(c) has been discussed by assuming chi(Q) to play an essential role for the occurrence of high-T(c) superconductivity. The T-dependence of 1/T1 below T(c) suggests strongly the d-wave pairing model.