Comment on "Correlated impurities and intrinsic spin liquid physics in   the kagome material Herbertsmithite" (T. H. Han et al., Phys. Rev. B 94,   060409(R) (2016))
  Recently Han et al. have provided an analysis of the observed behavior of $\rm ZnCu_{3}(OH)_6Cl_2$ Herbertsmithite based on a separation of the contributions to its thermodynamic properties due to impurities from those due to the kagome lattice. The authors developed an impurity model to account for the experimental data and claimed that it is compatible with the presence of a small spin gap in the kagome layers. We argue that the model they advocate is problematic, conflicting with the intrinsic properties of $\rm ZnCu_{3}(OH)_6Cl_2$ as observed and explained in recent experimental and theoretical investigations. We show that the existence of the gap in the kagome layers is not in itself of a vital importance, for it does not govern the thermodynamic and transport properties of $\rm ZnCu_3(OH)_6Cl_2$. Measurements of heat transport in magnetic fields could clarify the quantum-critical features of spin-liquid physics of $\rm ZnCu_{3}(OH)_6Cl_2$. 
V.R. Shaginyan, M.Ya. Amusia, J.W. Clark, G.S. Japaridze, A.Z.   Msezane, K.G. Popov
cond-mat.str-el