Atomic-scale quasi-particle scattering resonances in Bi₂Sr₂CaCu₂O(8+δ)

Low-temperature scanning tunneling spectroscopy of the high transition temperature (high-T(c)) cuprate Bi₂Sr₂CaCu₂O(8+δ) reveals the existence of large numbers of identical regions with diameters of about 3 nonometers that have a relatively high density of low-energy quasi-particle states. Their spatial and spectroscopic characteristics are consistent with theories of strong quasi-particle scattering from atomic-scale impurities in a d-wave superconductor. These characteristics include breaking of local particle- hole symmetry, a diameter near twice the superconducting coherence length, and an inverse square dependence of their local density-of-states on distance from the scattering center. In addition to the validation of d-wave quasi- particle scattering theories, these observations identify a source for the anomalously high levels of low-energy quasi-particles in Bi₂Sr₂CaCu₂O(8+δ) at low temperatures.