  We observed a large decrease of Tc by no more than 3 at.% of Zn doped to the
optimized superconductor LaFeAsO0.85 (Tc = 26 K), confirmed by measurements of
electrical resistivity, magnetic susceptibility, specific heat, M\"ossbauer
spectroscopy, Hall coefficient, and an electron probe micro-analysis. The rate
~9 K/% is remarkably higher than observations regarding nonmagnetic impurities.
The Tc suppression is likely due to pair-breaking caused by scatterings
associated with highly localized electronic state of Zn doped into the Fe2As2
layer. If this is true, the Zn result well accords with the theoretical
prediction that suggests a sign reversal s-wave pairing model for the Fe
pnictide superconductors, unlike other nonmagnetic impurity results.
