Van Hove features in BSCCO(2212) and effective parameters for Ni   impurities inferred from STM spectra
  We present a detailed quantitative comparison between theoretical calculations of the local density of states and recent experimental measurements of scanning tunneling spectra around Ni impurities in BSCCO(2212). A double-peak structure on the hole side of the spectrum at the Ni site is identified as the spin-split van Hove singularity in the band structure. The Ni atom induces local changes in hopping matrix elements comparable in size to the induced on-site spin-dependent potential. We find evidence from the measurements of order parameter suppression in the vicinity of the Ni impurity. These extracted impurity parameters can be of use in quantitative calculations of macroscopic response properties, such as the AC conductivity. 
Jian-Ming Tang and Michael E. Flatt\'e