Atomic-Scale Quasi-Particle Scattering Resonances in Bi 2 Sr 2 CaCu 2 O 8+δ

Abstract
Low-temperature scanning tunneling spectroscopy of the high transition temperature (high- T c ) cuprate Bi 2 Sr 2 CaCu 2 O 8+δ reveals the existence of large numbers of identical regions with diameters of about 3 nanometers 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 Bi 2 Sr 2 CaCu 2 O 8+δ at low temperatures.