  We have probed the effects of atomic-scale impurities on superconductivity in
Bi_{2}Sr_{2}CaCu_{2}O_{8} by performing low-temperature tunneling spectroscopy
measurements with a scanning tunneling microscope. Our results show that
non-magnetic defect structures at the surface create localized low-energy
excitations in their immediate vicinity. The impurity-induced excitations occur
over a range of energies including the middle of the superconducting gap, at
the Fermi level. Such a zero bias state is a predicted feature for strong
non-magnetic scattering in a d-wave superconductor.
