NMR study of magnetic and nonmagnetic impurities inYBa2Cu4O8

Abstract

We report ${}^{89}\mathrm{Y}$ and ${}^{17}\mathrm{O}$ NMR measurements on ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{4}{\mathrm{O}}_{8}$ doped with Ni and Zn impurities to investigate the effect of magnetic and nonmagnetic impurities on superconductivity and on the normal state. We find that Zn induces extra NMR peaks in both the ${}^{89}\mathrm{Y}$ and ${}^{17}\mathrm{O}$ NMR spectra attributed to nuclei near the Zn impurity while the Ni moment washes out the NMR signal from nuclei near the Ni impurity. The ${}^{89}\mathrm{Y}$ NMR shift from ${}^{89}\mathrm{Y}$ sites nearest neighbor and next-nearest neighbor to the Zn impurity can be modeled in terms of a Curie-like NMR shift from Cu sites adjacent to the Zn impurity. However, the temperature dependence of the NMR linewidths and modeling of the NMR spectra are inconsistent with a commensurate spin-density oscillation about a local moment induced by Zn or about the Ni moment. We find that the normal-state pseudogap is very locally suppressed over a range of just one lattice parameter.