Disorder effects in the quantum kagome antiferromagnet ZnCu 3(OH)6Cl2

Abstract

Motivated by the recent NMR experiments on ZnCu3(OH)6Cl2, we study the effect of nonmagnetic 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 17O 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 two-dimensional layers. ©2008 The American Physical Society.