ABSENCE OF MAGNETIC PAIR-BREAKING IN ZN-DOPED YBA2CU3O7

Cu-63(2) NMR linewidths in Zn-doped YBa2Cu3O7 exhibit a predominant co mponent proportional to T-1 in the normal state. We attribute this res ult to spin-exchange scattering of carriers from localized moments ass ociated with Zn impurities in the CuO2 Planes. The estimated moment-ca rrier exchange, J(eff) = 20 meV, is more than an order of magnitude to o small to account for the suppression of T(c) in this system via Abri kosov-Gorkov pair breaking. A suggested alternative explanation is pai r breaking by strong potential scattering from the Zn impurity sites w hich requires d-wave pairing.