Comment on "Spinless impurities in High-Tc Cu-prates: Kondo-like behavior"

The recent obervation of a Kondo-like temperature dependence in the Li NMR Knight shift in Ca- and Li- cosubstituted YBa2Cu3O7-d was attributed by Bobroff et al. to be evidence of Li-induced local moments in overdoped Y123. It is shown from Y-NMR measurements on Y0.8Ca0.2Ba2Cu3O7-d and heat capacity studies on Bi2Sr2CaCu2O8 that such a Kondo-like temperature dependence is an intrinsic overdoping effect quite generally present in cuprate superconductors which are free of strong scatterers such as Zn and Li. It is probable that Zn and Li only induce local moments in the underdoped pseudogap region and not in the overdoped region.