Yong-Jihn Kim and K. J. Chang
 Impurity Doping Effect in High $T_{c}$ Superconductors
(106K, revTex)

ABSTRACT.  It has been observed that impurity doping and/or ion-beam-induced
damage in high $T_{c}$ superconductors 
cause a metal-insulator transition and thereby suppress 
the critical temperature.
Based on our recent theory of the weak localization effect
on superconductivity, we examine the variation of
$T_{c}$ with increasing of impurity concentration $\rm (x)$ in
$\rm{La_{1.85}Sr_{0.15}Cu_{1-x}A_{x}O_{4}}$ systems, 
where A $=$ Fe, Co, Ni, Zn, or Ga.
We find that the doping impurity decreases the scattering matrix elements
for electron-electron attractions, such as
 $V_{nn'}=-V[1-{2\over \pi k_{F}\ell} ln(L/\ell)]$,
where $L$ and $\ell$ are the inelastic and elastic mean
free paths, respectively. Using the mean free path $\ell$ determined from 
resistivity data,  we find good agreements between our
calculated values for $T_{c}$ and experimental data except for Ni-doped 
samples, where  Ni impurities may enhance the pairing interaction.