Quasiparticle resonant states as a probe of short-range electronic structure and Andreév coherence

The recently observed properties of quasiparticle resonant states near impurities on the surface of superconducting ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+\delta }$ demonstrate that in-plane Andreév processes are either absent or phase incoherent. Analysis of the spectral and spatial details of the electronic structure near a Zn impurity also suggest an effective magnetic component of the impurity potential. Further experiments are proposed to clarify whether the effective moments of nearby impurities are correlated.