  The recent NMR experiments on ZnCu3(OH)6Cl2 motivate our study of the effect
of non- magnetic defects on the antiferromagnetic spin-1/2 kagome lattice. We
use exact diagonalization methods to study the effect of two such defects on
finite size systems. Our results, obtained without adjustable parameters, are
in good quantitative agreement with recent Oxygen 17 NMR data. They provide
support for the experimental interpretation of the presence of defects within
the kagome layers due to Zn/Cu substitutions. Our results also show that
disorder effects become relevant at lower temperatures, raising questions about
the experimental evidence for the absence of an intrinsic spin gap in the
kagome 2D layers.
