63CuNMR Evidence for Enhanced Antiferromagnetic Correlations around Zn Impurities inYBa2Cu3O6.7

Doping the high- $T_c$ superconductor ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{6.7}$ with $1.5\%$ of nonmagnetic Zn impurities in ${\mathrm{CuO}}_2$ planes is shown to produce a considerable broadening of ${}^{63}\mathrm{Cu}$ NMR spectra, as well as an increase of low-energy magnetic fluctuations detected in ${}^{63}\mathrm{Cu}$ spin-lattice relaxation measurements. A model-independent analysis demonstrates that these effects are due to the development of staggered magnetic moments on many Cu sites around each Zn and that the Zn-induced moment in the bulk susceptibility might be explained by this staggered magnetization. Several implications of these enhanced antiferromagnetic correlations are discussed.