Pair breaking by impurities in the two-dimensional t-J model.

Pair breaking mechanisms by impurities are investigated in the two-dimensional t-J model by exact diagonalization techniques. Analysis of binding energies and quasiparticle weight of pairs shows that nonmagnetic impurities are more effective in suppressing pairing than magnetic ones in agreement with experimental studies of Zn- and Ni-substituted high-${\mathit{T}}_{\mathit{c}}$ 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 dynamical spin susceptibility. \textcopyright{} 1996 The American Physical Society.