Rajiv Singh (UC Davis): Kagome Spin-Liquids and Nuclear Relation in Herbertsmithites

The Kagome Lattice Heisenberg Model is one of the simplest realistic spin models with a quantum spin-liquid ground state. We discuss the current status of our understanding of this well-studied model. The precise nature of the spin-liquid state and the existence of a spin-gap in the model still remain in dispute. We also discuss experimental studies of Herbertsmithite material Kagome-antiferromagnet ZnCu_3(OH)_6Cl_2. We focus on NMR measurements by Imai and collaborators, who have presented strong evidence for a spin-gap in the excitation spectra. Through a Numerical Linked Cluster (NLC) calculation of the frequency moments, we show that despite the existence of substitutional disorder in these materials, the high temperature nuclear relaxation rates are well described by the Heisenberg model.