Cu NMR evidence for enhanced antiferromagnetic correlations around Zn impurities in YBa2Cu3O6.7

TL;DR

This study uses Cu NMR to show that non-magnetic Zn impurities in YBa2Cu3O6.7 enhance antiferromagnetic correlations, leading to broadened spectra and increased magnetic fluctuations, indicating local magnetic moment development.

Contribution

It provides direct NMR evidence of impurity-induced staggered magnetic moments around Zn in a high-Tc superconductor, revealing the microscopic nature of magnetic correlations.

Findings

Zn impurities cause broadening of 63Cu NMR spectra.

Enhanced low-energy magnetic fluctuations are observed.

Staggered magnetic moments develop around Zn impurities.

Abstract

Doping the high-Tc superconductor YBa2Cu3O6.7 with 1.5 % of non-magnetic Zn impurities in CuO2 planes is shown to produce a considerable broadening of 63Cu NMR spectra, as well as an increase of low-energy magnetic fluctuations detected in 63Cu 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.