TRANSPORT AND NMR-STUDIES OF THE EFFECT OF NI SUBSTITUTION ON SUPERCONDUCTIVITY AND THE NORMAL-STATE PSEUDOGAP IN YBA2CU4O8

Resistance, thermopower, and Y-89 nuclear magnetic resonance (NMR) mea surements have been carried out on YBa2(Cu1-xNix)(4)O-8 superconductor s. Nickel substitution reduces both T-c and the pseudogap energy at al most the same rate as does Zn substitution, but unlike Zn substitution , there is no second peak in the Y-89 NMR spectra that can be attribut ed to Y atoms sited near a local moment. We show that this discrepancy is consistent with there being no local suppression of the normal-sta te pseudogap about the Ni impurity contrary to the case for Zn.