89Y NMR study of the effects of impurities on and between the CuO2 planes in high-Tc superconducting cuprates

We have performed Y-89 NMR, susceptibility and thermoelectric power measurements on the Y1-xCaxBa2-xLaxCu4O8 superconductor to investigate the effects of impurities between the superconducting CuO2 planes. The results are compared with Zn and Ni impurities in YBa2Cu4O8 that substitute primarily for Cu within each superconducting CuO2 plane. Interplanar impurities result in negligible pair breaking while intraplanar impurities lead to a rapid depression in T-c. This is consistent with two-dimensional superconductivity within each CuO2 plane and weak interplanar coupling. The Ca, La, Zn, and Ni impurities all lead to similar increases in the Y-89 NMR linewidth at 293 K with increasing impurity concentration indicating, contrary to previous reports, that an induced local moment is not responsible for the linewidth increase. [S0163-1829(98)02417-5].