  Recent STM measurements have observed many inhomogeneous patterns of the
local density of states on the surface of high-T_c cuprates. As a first step to
study such disordered strong correlated systems, we use the BdG equation for
the t-t'-t"-J model with an impurity. The impurity is taken into account by a
local potential or local variation of the hopping/exchange terms. Strong
correlation is treated by a Gutzwiller mean-field theory with local Gutzwiller
factors and local chemical potentials. It turned out that the potential
impurity scattering is greatly suppressed, while the local variation of
hoppings/exchanges is enhanced.

Strongly Correlated Electrons;Superconductivity