$^{17}$O Single Crystal NMR Study on S $=1/2$ Kagome Lattice ZnCu$_{3}$(OH)$_{6}$Cl$_{2}$

Herbersmithite ZnCu$_{3}$(OH)$_{6}$Cl$_{2}$ is known to be a promising candidate material hosting a quantum spin liquid ground state. The recent success in single crystal growth of ZnCu$_{3}$(OH)$_{6}$Cl$_{2}$ as well as the discovery of a continuum of spinon excitations using inelastic neutron scattering\footnote{T. H. Han \textit{et al}., Nature {\bf 492}, 406(2012)} have opened a new chapter in the study of highly frustrated magnetism. However, the mechanism behind the realization of the non-magnetic ground state in ZnCu$_{3}$(OH)$_{6}$Cl$_{2}$ remains controversial, mainly due to the difficulty in understanding the role of defects in its physical properties. Through single-crystal $^{17}$O NMR study, we identified multiple O sites with distinct local magnetic environments. The behavior of local spin susceptibility and spin dynamics observed at these O sites provide invaluable insights into the nature of defects and their potential influence on the kagome spin lattice.\footnote{M. Fu, T. Imai \textit{et al}., in preparation. Also see T. Imai. \textit{et al}., Phys. Rev. B {\bf 84}, 020411(R) (2011); Phys. Rev. Lett. {\bf 100}, 077203 (2008)}