Transport and NMR studies of the effect of Ni substitution on superconductivity and the normal-state pseudogap inYBa2Cu4O8

Abstract

Resistance, thermopower, and ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}$ nuclear magnetic resonance (NMR) measurements have been carried out on ${\mathrm{YBa}}_2$(${\mathrm{Cu}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ni}}_{\mathit{x}}$ ${)}_4$ ${\mathrm{O}}_8$ superconductors. Nickel substitution reduces both ${\mathit{T}}_{\mathit{c}}$ and the pseudogap energy at almost the same rate as does Zn substitution, but unlike Zn substitution, there is no second peak in the ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}$ NMR spectra that can be attributed to Y atoms sited near a local moment. We show that this discrepancy is consistent with there being no local suppression of the normal-state pseudogap about the Ni impurity contrary to the case for Zn. © 1996 The American Physical Society.