Impurity effects in the quantum kagome system ZnCu3(OH)6Cl2

Motivated by the recent experiments on the new spin half Kagome compound ZnCu3(OH)6Cl2, we study a phenomenological model of a frustrated quantum magnet. The model has a spin liquid groundstate and is constructed so as to mimic the macroscopically large quasi-degeneracies expected in the low-lying energy structure of a Kagome system. We use numerical studies of finite size systems to investigate the static as well as the dynamical response at finite temperatures. The results obtained using our simple model are compatible with a large number of recent experiments including neutron scattering data. Our study suggests that many of the anomalous features observed in experiments have a natural interpretation in terms of a spin-1/2 defects (impurities) coupled to an underlying Kagome-type spin liquid.