PAIR-BREAKING BY IMPURITIES IN THE 2-DIMENSIONAL T-J MODEL

Pair breaking mechanisms by impurities are investigated in the two-dim ensional t-J model by exact diagonalization techniques. Analysis of bi nding energies and quasiparticle weight of pairs shows that nonmagneti c impurities are more effective in suppressing pairing than magnetic o nes in agreement with experimental studies of Zn- and Ni-substituted h igh-T-c superconductors. Besides, we determine how the localization of holes contributes to the suppression of pairing. Finally, we examine the effect of impurities on the magnetic order by computing the dynami cal spin susceptibility.