A mean field t-J model for high T_c superconductivity containing two kinds of point defects

We describe studies of the effects of point defects on a t-J model of high T_c superconductors. One kind of point defect is associated with an enhanced value of J at certain randomly selected sites. The other kind of defect is associated with random values of the on site energy in the one-electron part of the model, as in the Anderson model of localization. We present a qualitative argument to the effect that such a model might account for the anomalous sensitivity of high T_c superconductors to nonmagnetic impurities in the copper oxide planes. We present numerical mean field calculations on the model in which disorder due to point defects is treated explicitly. A strong dependence of T_c on the Anderson parameter W is observed.